Thank you for responding.
In this case the registration will be mostly by people I don't know.
Like most people who have forums there's always a bit of wishful thinking and all that about it being popular. But this time it wasn't anything to do with wishful thinking, it was more like sober advice from somewhere. So, I figured best to be prepared than all of a sudden freak out with an overload.
It may not happen, it could be just another regular forum, and that's okay. But that feeling of being prepared just won't go away. Yeah, it's weird.
I recently upped my hosting to a different plan. Now I've got more space and bandwidth and also 50 databases (though I have no idea what the heck I would use 50 databases for.