I’d have liked to move this to the relevant thread, but for thread-historical reasons it’s locked away in the Plaza.
https://forum.choiceofgames.com/t/questions-about-patreon-use/48245
Anyway, the upshot of the back and forth there is that past authors have got the greenlight from CoG for using a Patreon to build a supportive fan community, offering stuff similar to what you mention.
I think you’ve got a good sense of what wouldn’t be allowed, and what would be OK.