initialy you posted in the common InDesign forum.
Someone—not me—with admin rights in the forum moved your question to a special subforum for InDesign that is dedicated to EPUB creation.
Hope, that's ok for you.
Now to your question:
Complex matter, I'd say.
All in all for EPUB creation I think you have to go with Fixed Layout EPUB, because you want to contain the integrity of content units that resemble "pages". But I'm not sure… That would affect the answer for # 6 on your list tremendously. Define "various e-readers" and maybe someone could give you a better answer than: "Hm. No. That's not easy at all…"
Is your product a commercial product?
Something you like to sell?
Answering this could make a huge difference to make suggestions for your workflow.
If no, try the "Publish Online" feature with InDesign CC 2017 or CC 2015.
If yes, I'd recommend a third-party plug-in for InDesign to shape your output to your desire.
I would look into In5 and its new capabilities for publishing:
The new version is out since yesterday and compatible with CC 2017.
Thanks for replying.
"Various e-readers" refers to things like the Nook and Kindle. I would certainly (of course) also like it to be readable on an iPad or desktop/laptop computer (using, I suppose, whatever software would be required on that device).
Yes, this is a commercial product which I intend to sell.
Thanks a lot.
My $0.02 is to just do two versions. What you're proposing would be nearly impossible with reflowable and an absolute nightmare of work with MSOs in fixed layout.