Is there a biological tech level you're expecting when building an FAI becomes possible?

I don't know. We don't actually need any technology other than Python and vi. ;) But it's possible uploads, cloning, genetic engineering, and so forth will be common then.

What do you mean by "naturally born"? Are artificial wombs a problem?

Yes, just to be safe, we should avoid anyone born through IVF, for instance, or whose birth was created or assisted in a lab, or who experienced any genetic modification. I'm not sure exactly where to draw the line: fertility drugs might be ok. I meant anyone conceived through normal intercourse without any technological intervention. Such people can be added in later if the CEV of the others wants them added.

It's conceivable that children have important input for what children need that adults have for the most part forgotten.

Yes, this is a really good point, but CEV adds in what we would add in if we knew more and remembered more.