Seeing as how it would take most people a year to reach 50 posts on the old forum, I think that the first milestone should be 20 posts (or at least something smaller). After that, I would suggest the next milestone to be 100 and then 200.
Possible sequence: Rookie, Vetran, First-a-holic
Based on the experiences I have had at other forums, getting that custom message is quite a milestone, enough that it causes people to post too much. To alleviate this, would it be possible to not make the custom message occur at a specific number of posts, but when a moderator thinks that a person has earned the right to stand out from the crowd?
This would keep people from posting too much just to get the custom title. It would also reward the people who spend thier time hear making meanifull responses.
In other words, you wouldn't get a custom message by only posting in the chit-chat forum
