Very nicely created book. Do you mind a few hopefully helpful suggestions?
1. The "descenders" on the title page are truncated. What I do to fix this is to add an additional line with some "centred" text on it immediately below the title, then delete the text but leave the (blank) centred line. This forces the Reader to add an extra blank line and you get the descenders shown correctly.
2. Your "Ch 1" is not showing up as a separate chapter. Its name doesn't appear in the page footer, nor is it is in the TOC. Try adding a manual page break after to "Preface" - this will probably fix it. There's a minimum length for a chapter below which BD doesn't treat a title as a new chapter.
3. Do you think that the page header adds anything to the book? I just think it's a waste of space, personally. Fine if you like it, obviously
Anyway, as I say, it's a very nicely done book. Well done!