Do chapter numbers start again at 1 in each part of my book?
No. In BookyAI, chapter numbers run on across parts: if Part I holds chapters 1 to 4, Part II starts with Chapter 5. That is the same on the book's page and in every export, so the contents page, the ebook and the audiobook all agree. Parts, available from version 1.9.24, are numbered on their own: Part I, Part II and so on.