ARGOS, I actually really really like that setup. It seems very good.
I would say, below a certain threshold, the poster must wait for an admin to approve the message posting. They can preview and everything, and then instead, when they hit "submit", it is checked for those criteria if their post count is below a certain threshold. If it matches those criteria, then it is stored and awaits approval for posting.
To speed it up, by the same logic, anyone who is part of the other group ("proven posters", you might say, lol), is allowed to view a page where they can approve the post. Or ya' know, maybe not