I would strongly recommend to start with as little categories and organisation as you can stomach.
Your users will spend a lot less time thinking about a topic’s taxonomy than you would like, that is life as a community manager. This book is an absolute classic for a reason: Don't Make Me Think - Wikipedia
I think that generally they are not needed and in most cases are harmful to a community. They are only unlocked with a hidden site setting for a reason.
I’ve always been enamoured by Jeff’s analogy from 2014:
I often describe Discourse as an interesting dinner party.
Think of categories as rooms, topics as tables, replies as conversations. Your goal, as the dinner party organizer, is to found your own successful restaurant
Don’t put too many rooms in your restaurant, it makes the place feel dead and empty.