I think anything like that should go into About the Python Help category as that should be pinned for everyone. And if you do want to do this I would work with someone like @nedbat who has a lot of experience from python-list and such on the wording.
Yes and no. Yes as in there’s a single place to block spammers, etc. No from the perspective that lately most of the admin work has been split between spam and misplaced posts that should have gone into Users.
I guess the question is whether people who are helping out in Users truly want it to grow, stay the same, or maybe even go away? I’m not sure if helping out here is better, the same, or worse than on top of IRC, python-list, etc.
As for the admin overhead, I would be fine with it as I would only admin the dev one 
. Not sure what @ambv or @pablogsal think about this idea.