Dare I say, where it all began is what happened before
(sorry not sorry)
We know the gap in time as Ocean has said it was 20 years. Even if we didn't have Ocean's timeline, or he changed it, we have to have enough time for Ayua to be a Zane baby from inception (no Zane is pregnant in WiaB) to college age. We've established this, and will probably have to keep passing the info down through the thread for people who can't find the dev logs buried between talk about video cards
Based on 20 years, Amber is going to get pregnant with Bella soon in Wiab's time.
Regards the presence of characters earlier, it is most likely we'll see them as easter eggs if they're not directly relevant ie Amber might not be there as a part of the plot in WiaB, but she might be there as a side character dancing at Leia's nightclub, or having drinks with friends at the bar etc. Or she might be a later part of the story, where we see her meet Mr Von Halen, who knows?
Something I've been cosnidering about the book club - so many of them are associated with interesting backgrounds. One thought I have is that some of the book clubs members might be ex working girls from Leia's club, and that might include Noji. We don't know anything for certain about what Katie's interest in Nika and Nami is, only that Noji has been going to the same bookclub with Katie and Leia for years as well as working with Scarlet. We might discover her connection to Leia runs deep in WiaB, but it'll be a while before we know anything like that, Ocean won't spoiler SG with WiaB and vice versa. The reason I think this is an interesting avenue for thought is when we saw Emilio in WiaB, suddenly we have all kinds of new potential plots or angles appear, and certain things seem more plausible (still creeped out by Desiree creeping through the college in the background).
Something about Marla - I think if we see her in WiaB, it'll explain why Nika is 'part of her problems'. She might have been a bystander during some of the events, maybe she saw what happened to the Cyrus's.
Finding these things out is impossible though, just like we never expected Emilio in WiaB, even if they appear, Ocean loves misdirection.