How can a single individual have over 12 threads on a single page that is supposed to hold a total of 38 threads and most of this posts are pasted on the forum the same day (within the range of 3 days).
As far as I know there are no limit to set unless you have a newbie jail. A user can make as many posts as they want and create as many topics as they want. That's not a problem. If you find something zero value, something that is spam immediately report it to the moderator. The moderators have a level of tolerance before they give the user a warning if not ban him. Few warnings without being changing the old habit then he will be banned today or tomorrow.