If the project was FOSS, it would have been interesting to follow the development and learn from it. But it being proprietary, I don’t see why anybody would be interested in it, TBH.

I would stay away from YAML (almost at all costs).

For us to be able to help you, I think you need to give us some more details about the organization of your work. If each chapter is a separate text file, then you don’t really need to do any branching at all (assuming people will only make changes on their own files and not touch others’ work). If it is a single text file, branching (or anything else, to be honest) will not help much.

I assume chapters will have their separate files. As long as you can control who touches which file, everybody can work on the same branch (also referred to as “trunk based”). But if you fear that people may interfere with each other’s work (willingly or by accident), then it makes sense to create a branch per chapter to keep contributors at a distance from each other. But working on a single repository requires some sort of an agreement on the workflow.

Careful with Paul. He may starve.

Who is Paul? Why is he killed? So many questions. And I’m still stuck at the chess board…

OK, I may have hit a wall with this one.

I think I will quit at this point.

That depends on the PR tool. I don’t know how others work, but Azure DevOps handles rebases quite well (as long as you are rebasing to the target of your PR).