Thanks for the thoughtful replies and useful information. We have InDesign CS5 and clearly should upgrade. It might be simple, but clearly I have a lot to learn. I will spend as much time as I can spare reading relevant posts here.
Thanks also for the recommendation of lynda.com. Rumor has it that we will be signing up there and possibly bringing in someone with lots of epub experience. I won't hold my breath, but it's nice that people are beginning to appreciate that this will be more than a mouse click.
None of the maps have yet been created, since the project is still in the early stages, but no doubt will create many questions as this thing unwraps.