Sounds good!
I’ve used NodeBB before for similar things (though my personal one is down right now), since it’s easy enough to host for free. I believe it can connect with Misskey and bluesky (though bluesky requires bridgy.fed to work).
For the questions on the setting: I’ve mainly got 2 major ones
- Which demi-human species (elves, dwarves, etc.) are present? Feels like the right kind of setting feature, but I wonder how many becomes too many for a creator to need.
- Would it make sense for portals between worlds to appear/work at rare times? I could easily see that allowing for users to justify new characters within the setting easier, but that may be good or bad, depending on the intended vision.