They're still many light-minutes away and that merits a thought-out response so it'll be a while before there's an answer. Eventually one of the Precursors writes something with his mail label. (And if he's checking his entire inbox, multiple other people have also written him letters.)
He was at war with the metal heads. There was already a market for their skull gems. That he sold his to the oracle is hardly worse than if he had sold them to a jeweler or used them for interior decoration. That said, it would be helpful to the oracle if you could, and would, provide it with skull gems. They are somewhat useful to its maintenance and make it slightly more able to do things like teach people to use eco more effectively and with more self-control.
Time travel is an extremely complicated topic which this language does not even have a good vocabulary for. Further, communicating with people about it is annoyingly tricky even when there is a shared vocabulary.
The oracles were left behind on that planet long ago. They are not from the future. They have access to all our information about the planet they are on, some of which may come from the future, but they themselves only see what is already in the present. This may include, for example, the way an old man from the future talks to a pair of children about dark eco. They have some ability to draw inferences, but they are not omniscient.
If the Precursor egg is hatched, the resulting Precursors will gather strength and fight the dark makers. I cannot impress upon you strongly enough how important it is that we stop them. Unless there is some misunderstanding of an even greater scale than that with the metal heads, they want to destroy everything, preferably in a way that involves exposing life to dark eco before it is destroyed.
Also, if the egg hatches, there will stop being an ancient unhatched egg in Haven City. I must warn you that the destruction of any one of our eggs from that era has a several percent chance of causing the destruction of the entire universe. We are working on fixing the design flaws that make this possible. We have already made it much less likely. We do not expect to need to reproduce again before we have solved it entirely.