Hi Katherine,
this sounds all a bit weired and will get complicated. E.g. I did in the past some same projects, but since modern laptops have no cd drives anymore, those linking PDFs are not the way to go. As you can imagine, it is always a good idea, to have all interactivity in InDesign already, but things like rollover popups can only simulated with object states and buttons. I’m not sure, if this behaves like rollovers with JS at the moment.
What is cloud-based content management? InDesign has no API for that … infact, this is not true, cause you could third party plugins to link e.g. to google docs or connect InDesign with wordpress. DRM is not very common in europe anymore. We use soft DRM instead of hard DRM. If you want to go with epub, everything will be more complicated, cause of the lack of interactivity and page geometry.
So it seems, that you should inform yourself, what is possible today in 2019 and what cannot be done.
best
Kai