Okay I crunched the number thanks to the page numbers we saw. (This is based on if Veyle is the first character in the Gradlon section of the book)
We can expect the sections to go
Lythos - Firene - Brodia - Elusia - Solm - Gradlon.
I'm making the assumption that Yunaka and Anna comes after the Lords and their retainers (because of the marketing we already have), so 8 pages (double spread for each lord and normal page for each retainer) and then 2 pages for Yunaka/Anna + Saphir/Lindon.
Meaning that between Saphir and Ivy there is another 12 pages. Making it 22 pages for Brodia.
If we take that 22 pages and apply it to Elusia we go to page 119. If we take 22 pages and apply it to Solm starting at page 120 we go to page 141 making the next page, 142, the beginning of Gradlon with Veyle.
So we probably can deduce that each of the 4 kingdoms as 22 pages dedicated to them, but I don't think we'll have 20 playable characters from each kingdoms (2 double spread + 18 normal page). So after Saphir and Lindon the rest of the pages could be a mix of playable character, NPC and landscape art of the kingdom.