Ok - the Advice section ready for release, by which I mean the Klingon Programmer's Code of Honor definition of "release" (bullet point 5).
I've consolidated all the chapter documents into a single massive 250-page-plus document. This is one of the weakest points in Affinity Publisher, but we'll give it a shot because it should enable a much smaller file size. Seriously, Affinity, book docs. Seriously. You are not building a better workflow here.
My next steps are fixing the "page xx" cross-references, making yet another layout pass for all the styles that broke during the document merge, and sending it to the proofreader. I also have to (ugh) make decisions about uniform capitalization (or lack thereof) for game terms.
As part of this I'll be posting a Release Candidate version later this week.