I really like this idea, but I wouldn't make it a set number of posts. Instead, Ithink that a 2-week ban on creating threads would suffice. This would allow the newcomers the opportunity to read threads, answer some of their questions before hand and allow them to become more knowledgable as members. (It would also allow mods to not have to deal with spamming Threads as it seems most spammers flood the site within a day or two).

Another thought, is to decrease the amount of threads one can start per day. Saves space, keeps people from having to go through more than a few threads about the exact same topic.