In reply to Andrew Langley.

Dang, thanks so much! That's even more helpful than I was hoping for in my best-case response.

I think you're absolutely right as to the overall configuration -- inputs attached directly to the Pi, and a Feather board driving each smaller display. If for no other reason than that is the perfect answer to my last question about dividing-and-conquer until I know better what I'm doing. The Adafruit examples show how to set up a single display to a single Feather, and I'm sure that there's no shortage of beginner tutorials about hooking up individual buttons and potentiometers to the Pi. (Not to mention that it would make it possible to run the smaller displays independently, triggering sequences from the master Pi controller).

Thanks again for all the info, and for making me optimistic that I might actually be able to get something working!