@Freemind have already provided you with links to learn more about the forum and the question you asked, but regarding the minimum and maximum posts you can do in a day, that totally depends on you, man. If you can do 20 to 30 posts per day, you are welcome, but make sure that you are not spamming, shitposting, or plegarizing.
Also, on the forum, I don't think you should be very concerned about your rank; just be an active member, contribute positively, and you will archive new ranks, respectively. If you are too concerned about the ranks, you might only end up not being a quality contributor to the forum.