Wow! Thanks for the feedback, y'all! And, yes, picture STORYbook is exactly what I was thinking! As for chapter length, it's hard to break up a scene in the middle, so the longest chapters are just over 4 pages while the shortest are 2. That's about 10 chapters. Looks like I need to add a couple of transitions here and there since I'll be going with chapter breaks.
I think I've decided on size 8x10, font size 16. I am thinking of varying images at least three ways: (1) an image that takes up 1/4 of a page on a two-page spread, (2) half-page images (either on one side only or spread across both), and (3) a whole-page image facing a text-only page. I seriously doubt I'd have any whole two-page spread images. It's looking like I might have between 50 and 60 pages of actual story with images (IOW, not including front or back matter), which I don't think is too terribly bad.
Why, oh, why do I insist on challenging myself? At least I have a decent idea of where I'm going after all of this brainstorming. Thanks for the valuable input.