I'm currently reading the iBookstore Asset Guide 4.7 Rev.3.

It seems my first problem was not including all the book elements in the <guide> block.

I'm also surprised to learn that page breaks do exist! I hadn't had any luck with InDesign's keep options, so this is promising:

To indicate that a page break should come before or after an element, set up a style in CSS using the
page-break-before or page-break-after properties. Accepted values for these properties include:
■ auto: Insert a page break before or after the element as necessary
■ always: Insert a page break before or after the element

I've not attempted getting my book into iBooks yet, but I've been testing embedded video in the epub on iPad. It sorta worked. I think I've run into the InDesign CS5.5 webkit bug due to my non-breaking spaces in my ellipses. If you end up having any "shy" or %nbsp; errors, you should google that bug to fix it. 

Anyhoo, which version of CS are you running? If you are using CS5.5, page breaks are effortless. You don't need separate files in a book. You can have your book in one file and use TOC/paragraph styles to tell InDesign where to page break. CS5 requires "books," I believe. I can't remember now…

But either way, you don't need to use CSS to break your pages. Let InDesign do it for you.