To resize the book, switch on "layout adjustment" and change the page
size in the document setup panel. You'll probably have to do this
separately for each document, but I usually avoid the book panel, so
maybe there's a shortcut there I'm unaware of.
To easily change the leading of all the paragraph styles from an old
value to a new value (as well as changing any related measurements, e.g.
a subheading which has ×2 the leading, and some other helpful features)
you can check out a script I sell on my website called "Change point
size and leading". Look under the "Scripts" tab on
The alternative is to go through all your paragraph styles and do it
manually, which is a schlep.
Have you tried making the changes on your Style Source document (document set up, margins, paragraphs style, etc) and then sychronizing? Just make sure you keep a copy of your original!
That's not likely to work. Books can contain documents with different page sizes.