Could you dream reading books teaching science you don't know? Would the books be accurate? How long do conjurations last?

Books conjured from dreams only contain whatever information your brain generated to put in them. Conjurations need to be maintained--so, as long as the conjurer is able and inclined to hold them.

Is there a limit to how many, or how complex, you can have at a time? 

Yes and no. There's no hard limit, but every dreamshaper has their own limitations, and expanding what you can do takes hard work and practice.

They'll ask questions well past the Mingling, at which point Maitimo will make his excuses. "Someday the King is going to lock the gates of the city on me."

"You can climb the walls," Ambarussa offers. 

"Wisdom I will bear in mind but not court opportunities to put to use."

"Thought you mostly didn't use locks?"

"We don't! Tirion's gates have never so much as been closed but if they ever are it will be this family's fault, mark my words." 

"Why does Tirion even have walls and a gate?"

"Force of habit! We'd lived beside Cuivienen, we were terrified, when we got here the Valar asked us 'what will make this place a paradise for you' and we said 'really tall, really thick walls' and they provided, though there are no dangers here. It prevents the city from sprawling out across the entire surrounding area, which has something to be said for it."

"Cuivienen?"

"Tyelcormo what did you spend the last several months doing?" says Ambarussa, and his twin giggles.

"The Elves awakened and lived for our first while as a people - we didn't count time back then, we aren't sure how long - besides the lake Cuivienen," Curufinwe says. 

"Awakened?"

"The whole story," says Feanaro, "tells more about the tellers than the truth, I think. But that the first Elves awakened fully grown, placed there by Eru, is a common thread of all accounts and memories."

"Huh. I have no idea how my species got started."

"Your creators are less active," he says. 

"I don't know if we even have any. I suppose it's more likely, given that this place exists."

"How would you have come about otherwise?"

"I don't actually know. But we have stories about gods, and no actual solid evidence for their existence, and none of the stories agree about anything enough that I'd be confident that that theme was an aspect of what really happened."

He nods. "Well, here the gods have opinions on many subjects, and are often right about the factual ones."

"It has been explained to me that they have values not actually compatible with what's best for people. I'm sorry about your mom."

"Thank you."

"I don't--claim to understand everyone's motivations, there, I didn't get a lot of explanation on anyone's motives beyond the obvious, but that was a deeply shitty thing to do to you. And her."

"Understanding the motives of the Valar doesn't work. I spent a long time attempting it. They do not think sufficiently like us."

"Huh."

"It makes ruling us a great challenge to them but has not deterred them from attempting it."