I think I would vote for something widely used like phpBB because of the multiple add-ons which allow eg. busy threads to pop up on the homepage, announcements, polls etc.
I ran a phpBB site 15 years ago for a customer, from my home, it took about an hour to get it working. I expects it could be deployed on a Raspberry Pi these days.
A mistake NOT to make is to deploy it on the same hardware as maintainer email or software archives, because if either of those go down the forum would be the place to discuss bringing things back to normal,
Edmund