Another thing he discovers is that you usually can’t become a cleric without praying to a god. Which is important and affects his next actions.

A topic is important to consider, before planning anything else.

What structure does this world have? What shape do events have in it? What kind of a person he is now? What kind of person he should chose to become? Though ultimately the last two questions are the same question, the person he is will affect what person he will want and be able to become, and the person he will become would be the one he was supposed to be all along, that’s how metatemporality works...anyway.
"What kind of person is he now" is a question deeply entangled with "what god would he follow". Well, he will probably pray to many gods, many are fine, it doesn’t cost anything. But only one god he can chose to be a cleric of, or generally ask directly to do something important, to choose cooperating with as the main mission of this life.

A vague intuition, on the corner of his awareness, tells him that there is a god for whom his state in Selensia (and several other worlds which are like Selensia but he doesn’t remember as clearly as Selensia), "franticly running around screaming at stupid people and knowing this won’t help and they end up destroying everything", is the exact thought pattern for ideal alignment. But he doesn’t want to live this way again. It’s stupid to deny reality because he doesn’t want it to be true, but this is one of the rare cases where what he wants is actually important.

"One who heard the all-powerfil call of magic can’t be stopped by anything"…except those are Raistlin’s words, and he doesn’t want to be similar to Raistlin in any way…except the fact Raistlin was an extremely powerful wizard, which is a good thing, and exactly what the quote was about in the first place…
If it’s one of the worlds where Raz, by definition, by property of the world and his existence in it, can’t do anything meaningful, can’t affect any large events…and most worlds, around 80%, probably, are like this…than there is no point in making complicated plans and calculating how to maximize his positive effect on the efficiency of the world. He should do the things he gravitates to naturally, the things he likes. Which means Nethys. Curiosity is one of the few emotions Raz has left, and discovering new things, thinking about interesting concepts, realizing how all the patterns fit together, is one of the only things Raz can be said to truly – in the meaning that normal people use when taking about normal people – enjoy.
Nethys-assisted/directed research of magic and universal laws could also turn out to be instrumentally efficient, but most probably it would be less efficient than anything else. Knowledge of different worlds is usually not directly applicable, due to different universal rules; Raz has good instincts and habits for learning new principles of magic, by virtue of learning them dozens or maybe hundreds of times, but most of his previous magical knowledge is not useful in Golarion, and knowledge of Golarion will probably not be useful in later worlds. And even learning optimally, Raz would probably not be as good at magic as some other existing wizard, he would just be another somewhat powerful wizard. Maybe...fourth or fifth circle, if his intuitive understanding of local magical levels is correct? Not bad, but not enough to make a difference. So if he wants to make a difference, that is probably not the way, and his knowledge would be better used by someone else, while Raz engages in trying to coordinate some large scale philosophical/economical change.
So, back to the origin of the thought, Nethys is only a choice If Raz doesn’t care about his impact upon the world. But he suspects, based on many things, none of them easily describable, that this world is a world where he can have an impact, can change things. Not…fully? Not on a deep level? Not the true world? Not..all versions of the world? That’s probably it. There are multiple versions of the world, most of them will continue in the original direction, but in one of them, the one he feels and perceives around him, things can become meaningfully different.

"Magical research that creates new useful tools and abilities" might be an Abadaran thing just as much? Creation of wealth and value through work. maybe. Raz doesn’t fully understand Abadar (or rather, has several possible models that aren’t fully consistent with each other).
Raz believes in mutual benefit, is extremely honest and wishes for existing systems to be fair. Is that enough for fitting the god? And will the god's help be maximally useful? Those are two separate questions both of which he needs to think about.

[The specific thing Raz focused on, as part of himself that may be aligned with Abadar, the desire to build and improve things, would be perfectly aligned with Aroden. But Raz didn’t read much about him, and Aroden is dead anyway.]

Iomedae. Fighting evil.
Raz mostly conceptualizes himself as someone who "prevents harm" or "creates value", rather than "fights evil". And declaring a war on evil as your main goal is a dangerous thing to do, because the definition of "evil" may drift between people and across time (as he saw many times).
But evil does exist. And fighting is necessary to protect people. He isn’t a pacifist. He took "fighting is necessary" too far in his first life (partially because of Buss. If you are listening, screw you Buss, for all your failings), but it’s a correct principle.
Various monsters in Golarion are evil and destructive and must be fought.
Is Raz good at fighting them? Not especially, though he is especially good at being brave (or rather, not feeling fear), and sacrificing his life for others (even if his life was an exhaustible resource. Which it isn’t).
There are probably suicide missions he could take in the end of his life (if he doesn’t die randomly, as often happens) to help Iomedae’s church, or servants, or people who believe in her generally, without directly being her cleric.
He is also a little instinctively suspicious of the way Iomedae’s ideology approaches rules and laws (it sometimes looks like naïve-deontology rather than pragmatic-deontology), but laws are necessary to fight wars efficiently and minimize harm caused by them. 

Irori. Self-knowledge and self-perfection, the endless path of learning from your mistakes.
Raz is...already on his path. His ideal is already in trying to be as coherent and as correct as possible. He doesn’t really aspire to become better, though, because he doesn’t think he can. He already reshaped himself to be the best version of himself he can be. (Which is not a lot! He is not that smart, or that rational, or that knowledgeable, compared to some other people he met. It’s very disappointing, that this is his best. But "things can never be ideal, but can always be optimal", as the saying goes). And if there is some opportunity for improvement (external or internal) that was not available before but Golarion can offer, he couldn’t keep it in his next life anyway. He would still have the memory and knowledge, but not the improvement itself that results from the knowledge, habits or instincts or abilities.
But maybe, even if limited to this world, there are specific divine-magical abilities that Irori could offer that he can’t have any other way, that would complement his existing skills and habits and thoughts in a way nothing else will, and Irori will give them as recognition of the Way he already walked? Though probably that wouldn’t be more than any of the other three gods will recognize as already doing a lot for their interests and values. Maybe even more than Irori.
But…other gods seem to already largely have what they want to an achievable extent? Lomedae has orders of paladins that fight evil. Abadar has a country and priests writing essays on economy, and Raz doesn’t know more economy than them. Even if he himself built some systems that achieve Abadaran values, they would have done the same with his resources and circumstances. Nethys already has complicated magical things that happen, and also presumably infinite other worlds. Maybe he will even find Buss somewhere, and they will bond over their mutual love of chaotic magical processes and complicated explosions. And Irori…Raz doesn’t actually know of orders dedicated to him, what texts and ideas and teachings they have on how to achieve mental perfection (they are probably good at physical perfection, something Raz knows he is not good at), or what goals Irori has in the larger world. Does he want all people to be perfect at logical reasoning, not making any mistakes, recognizing their desires, shaping themselves to be the kind of people they want to, achieving enlightenment in regards to their own feeling about the world?
He should know more about it. Except he doesn’t really have the time or opportunity for getting this knowledge, for logistical circumstantial reasons.

In terms of his very old motivation/value pointers from Aven…Iomedae is Light, Irori is Dark (which is a perfect example of the way in which Dark is not evil), Nethys is neither, and Abadar is possibly both? Or at least, there could be an Abadaran ideology that is both? Equal parts desire to be wealthy and safe and achieve your goals, and desire for other people to be wealthy and safe and achieve their goals? Mutual benefit sought both individually and collectively? That seems like the best thing? He wouldn’t get the spells and powers he really wants from Abadar. That’s his goal but not the best tool. Irori would be better instrumentally. Or Nethys. But Raz couldn’t trust their goals to be perfectly aligned with his, despite a big overlap.
Technically he wouldn’t perfectly overlap with any of them, unless there was a god who is perfect combination of all 4. Maybe not perfect, maybe 35% Iomedae, 30% Abadar, 20% Irori and 15% Nethys? Seems about right. That’s the kind of god that he himself would have been (and presumably, therefore, the one who would fit him the most). And in some sense been already, for some very specific value of "been" and "already". Not that it’s a useful direction of thought.

[if Raz fully understood the domains of Sarenrae, mainly "knowing that evil is a mistake people make and not an inherent property, and that everyone fundamentally deserves happiness, no matter who they are or what they did", he would include her in the list of potential deities to think about. But he saw "healing and kindness to people", and concluded, as he did many times about similar things "great that this kind of Light exists in the world, but not something I myself can do".]

Again a vague intuition, on the corner of his awareness, tells him that if he has an idea of a god he would follow without hesitation, believe in fully, consider impossibly perfect, he should actually pray to this god, rather than gods who cause hesitation, even if that god doesn’t exist. Because maybe the god would be created? No, unlikely. This is not an unshaped world with mutable reality. But maybe the god already existed, but was weak and without worshipers, and Raz will now awaken it? Or maybe the gods he knows of already fit him perfectly, in their true nature, rather than flawed linguistic description, he just doesn’t know it yet?
And even if he still must choose only between the existing options, he shouldn’t fit his values to a god. He should present his values, and then let the god who fits them best to decide. This is, intuitively for him, how divine communication should work.

He thinks about New Isengard. A place where things were good. Where people made each other better. Where the system was built in a way that helps the people and the people help the system. Constant chain of improvements.
Where people see that all the reasons for harming each other were stupid, and not actually good for them, so they stopped. Not just through building a Lawful society with the right kinds of incentives and tradeoffs and mutual benefit (though that’s important too), but by understanding of their emotions and values, of how the society works, and the nature of morality and desire (which are, in truth, one thing, because "good" and "bad" are categories people give to what they want and don’t want) work.
Where new discoveries were made because people looked where no one looked before. Because they shared knowledge, worked together, "stood on the shoulders of giants", while also being the giants.
Because they knew what to do, because they had the knowledge, but also the assumptions, the spirit, the…Understanding, of how things are. Understanding that was open to everyone. Information that was available to everyone. The same discoveries were made hundreds of years prior, but no one knew about them! One mad wizard discovered a secret, didn’t tell anyone, died in an accident. So pointless. Knowledge is meaningless if it’s not known to everyone.

He thinks about what he wants to do with the world. Make it better, fix all the things that are horrible. Except he isn’t good at it, really. He isn’t very good at noticing things being bad (as opposed to things he personally doesn’t like), because he inured himself to badness, intentionally, to be able to live, to endure being alive. Because he doesn’t like to fight evil, even if he has to. Because most of the problems in the world are not caused by nature. Or rather, the problems caused by nature are easy to fix, if people coordinate. The main problems are from people not coordinating (both in apathy, and in actual war), or from people creating problems for themselves, because they don’t understand themselves and the world.
Because they don’t think coherently. Because they believe they have to suffer from things that are meaningless. Because they believe they must harm others, over things that are meaningless. Because they don’t understand that everything is meaningless, unless they choose to give meaning to something. And that they would be happier if they only give meaning to the things that make their life better and happier.
And they lose themselves in tangles of beliefs and opinions and hostilities and prejudice that is, if you look it from outside, pointless and very simple. But no one sees it. No one but him. Even the greatest scientists and scholars and sages, who were smart, who could solve problems and understand ideas that Raz can’t, never truly grasped it. Some of them were able to articulate the principle, and understand why it Is essential, but couldn’t live by it, couldn’t even realize thewy are not applying it to their lives. And so wars started between people who Raz knew, who he was good friends with, despite both sides largely having the same opinions and beliefs.
Because becoming stronger is not enough. You can be a hero, and know all the secret magics and physics of the universe, and achieve your stated goals, but still be unhappy and still cause the universe more harm than good, because of how your actions affect other people.

And that is the thing that Raz can see, can, maybe, fix. There is no one else. The thing that Raz actually wants and is good at, naturally, rather than by circumstances…
No, that’s not really correct. He doesn’t want it. He doesn’t want anything.
He doesn’t want to live even. Though he doesn’t want to die either, he is not as weak to be harmed by life. To suffer from things that have no good reason to cause suffering (and there are no good reasons for it at all). There isn’t anything that can cause him to feel bad. That’s why he endures those….centuries, maybe millennia, of life.
Because he understands. He is not smart, and not strong, but he understands. And he can share this understanding. Can try to, at least. It never really works. The other things, the research, the wars, the projects, that works, sometimes. But it is only instrumental, only the second best solution. It’s things that wouldn’t be needed if the real, main thing worked. The actual, complicated and paradoxical, but fundamental understanding.
Him having it means he doesn’t need anything from life, but other people do, and that is exactly why he keeps living, despite not having the real internal reason to.
(From a very distant memories, of his first life, or even the zeroth one, comes the word "bodhisattva".)
He is not capable of love, but he lives only for others, as unselfishly as love can (maybe) never cause.
He was never capable of being happy, but that helped him find the understanding, that if shared with others, can maybe make them happy. He hopes. That is the only reason he continues.
He wants everyone to see it. To understand the world and themselves. So they can be happy.
That is the thing that guides him. The understanding, the drive towards making others understand, to make the only possible world in which people can be happy, because they understand themselves, and how to not make themselves or the world worse. Is this world possible? Can it ever be achieved? He has no hope, but he doesn't need hope, he will persevere, that is the right action, and he takes the right actions.

If there is a god who tries to do the same thing, who sees the same fundamental problem, who tries to fix it instead of just its symptoms, Raz would like to be the cleric of a god like that.

There is, as it happens, a god like that.