You could have all discussions for a particular category in a single forum and use the prefix to let the thread creator indicate which state.
You could have all discussions related to a particular state in a single forum and use the prefix to let the thread creator indicate which category.
I see state, category, and discussion forum - nice to get at least one of those handled with a prefix rather than another level in your node tree.
This is what I'd call a "data design" issue - you need to figure out a way to organize things that's maintainable. 6000 forum nodes doesn't sound maintainable, especially if when you decide to change something, you'd have to change it in a lot of "parallel" places. Your solution has to balance your need for granularity with real-world considerations of managing your forum.
Hope this is helpful.
-S-