MyBB Community Forums

Hello Users of MyBB, I am interested in knowing about this possible feature or mod...

I would like to take users who have not posted only able to see ONE forum that I specify (in this case the new member intros forum) and once they make a post there they can see the entire forum, Or should I accomplish this with the existing "Promotion" feature.

Also.... How does promotions work? Cron?

Do it with the default mybb feature.
Allow members in registered group only to view / post in introductions forum.
Give promotion to the members in register usergroup to another usergroup as soon as they complete one post.