Like I said above, I can see the benefit of a category setting limiting the number of topics a user is allowed to post in a category in a given time period. But there is no such setting currently, and I am not aware of any other customers requesting it or having rule of three.
Have you tried the “slow mode” category setting? I’ve not used it but it seems to be what you are looking for? You could set it to 30 days, so users are only allowed to post in the category once every 30 days. Though it appears to not slow down the starting new topics in the category, only replies. You can also auto-close topics so there are no replies permitted at all.
More about slow mode: