After a lot of hours spent watching InDesign how to videos, and struggling to get an epub to look right on the computer monitor I actually made a lot of progress only to find that what adobe showed as the output didn't look anything like what appeared on my ipads, either the old one or the retina screen version. Seems that epubs are really for text type books, not image intensive publications.
Someone sugg. checking with David DuChemin and Craft and Vision ebooks. Turns out they are all pdf's. I checked with a few other sources - pdf's - beginning to tell me something here.
So, I'm not abandoning my intentions to produce an ebook, but I will be doing it in PDF format. Downside is that you need a different version for each screen, but that wasn't all that diff. from epub anyway so not much of a loss, and I can show images properly on screen.
I have the latest edit back from Blurb for my 12X12 book - actually very nice, but at $137 it's incredibly expensive. I'm going to explore more reasonable options.
Anyway, look for a pdf format ebook suitable for the ipad in the not distant future.