Thanks @Bas!
A few extra insights into how we got to 3 categories (only 2 of which users can create topics in). I know cutting back on categories can be hard! 
We had 16 categories when we first launched our forum—each based around a conversation style: “Ask a question”, “General”, “Feedback”, etc.
Not only was it frustrating to manage and make sure everything was organised correctly, but it was also frustrating for users. We saw a month-over-month decrease in engagement and activity—simply because topics were incorrectly categorized.
We moved from “conversation style” categories to “intent-based” categories and have seen significant increases in engagement and retention.
We asked ourselves why people came to our forum, and it all boiled down to asking questions and showing off projects. We then use tags to separate topics within categories (e.g., “code”, “design”, “cms”, etc.).
A little preview into our thought processes:
