Thank you everyone, for the timely and informative replies. It’s all been very helpful, and I’m sorry for not responding more quickly. I’ve been watching the videos on Lynda.com (they’re excellent) and looking at Liz Castros blog. I was able to get a working, almost-acceptable, reflowable epub made, but due to time constraints, ended up having a professional finish the work for me. XD He’s done a great job tidying up my amateurish attempt and given me some good advice as well.
I may practice creating a fixed layout epub (which would be exported as a PDF, if I understand correctly) with a very image-heavy family book that I have set up in InDesign, just so I can see how that works. I’m pretty sure that one would not be suitable for anything but fixed layout, as the placement of images is extremely specific and rather complex.

I am learning a lot of new things thanks to you all pointing me in the right directions, and will continue to learn as I go.
(Code is not as scary as I thought it would be. It was actually kinda fun once it stopped looking like an alien language. Still confusing, but fun.)

Thank you again for all the help!