I use Discourse mostly for my TTRPG campaigns. They hold all my session notes from various games over the years. I have tried to encourage conversation between my players outside of the games on various categories in Discourse, but most of that chatter (chat, really) happens on our corresponding Discord server.
Ideally, my gaming groups would only use my Discourse setup for chat and the like, but you can’t beat the ubiquity of Discord among gamers. That, and the voice/video functions.
My preference would be Discourse because user generated data in Discord is something I inherently distrust and would like all the data on my own hardware without anyone else snooping (not saying that Discord does…)
I am not actually in the use case you provided for the AI-powered Q&A, but I thought I would chime in on the other items. 