On most sites, like the 501st detachments or the old ASAP site, there are lots categories, forums, and sub-forums. Dozens or even hundreds are not uncommon. Those sites use the forums for more than just discussion; they use them for organizing reference material, information, tutorials, images, and so on.
But here we have the costume guides, reference galleries, and the tutorials database. The forums should be for discussion.
Although its nice to have lots of specific forums from an organizational stand point, it usually results in a lot of forums with little to no activity. This causes people to avoid checking them very often creating a cycle, and often leads to a lot of unanswered questions from newbies.
Having to few forums can create the same problem. Recently the RPF split Star Wars, Marvel, and DC comcis costumes and props off of the main prop and costume forums into their own forums. It was getting to the point that posts, if left unanswered, would be on page 10 after the first day and would require lots of "Bump" posts to get any attention. I think that is the model we should follow. Start out with just a few forums and allow them to grow based on demand.
The Wookiee formerly known as JediToren