@cpcode welcome to the fun… you’ve done a good bit of the analysis work.
as you’ve seen, very little interactivity is provided today
there is a keyboard module https://github.com/lavolp3/MMM-Keyboard
but thats such a tiny part of what you want to do…
MM is a web page, so you can do it. .
maybe managing the content and form are doable in the JSONFORM library
https://github.com/jsonform/jsonform
I use this in my MMM-Config module for customizing MagicMirror config.js without editing
I’d store this kind of data in a mongo db, its all json, don’t have to do sql
then there are modules that can display from json
apis to update whatever source are the challenge
accessing from phone is possible with jsonform too… its just a web page
I use OurGroceries and Mealie as well.