Hi @Watercolor_Games, first of all, best of luck with your project from a fellow gamedev community manager. 
It’s a tough but rewarding endeavor, as I’m sure you’ve already noticed.
So for the Discord piece, the Chatroom Integration Plugin (discourse-chat-integration) should suit your needs. I use it on my own forum(s) to do exactly what you’re describing here.
One thing to consider though, either as an alternative or an addition, is Babble - A Chat Plugin. I mention this because although Discord is great and obviously very slick, you don’t own any of the data or relationships that come of it. That’s not to say it’s all out bad, but definitely something to consider. There’s also something very nice about having chat live on top of (or “within”) Discourse, including its self-moderation features (flagging) and even just a paired chat/forum in the same UX.
As for categories, try to avoid the temptation to over-categorize. I learned this the hard way despite others warning the same, and it would have saved me a lot of work if I had just put more thought into properly using tags instead.
For plugins, check out #plugin if you haven’t already. There’s lots of cool stuff there. In particular though, I would recommend:
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for moderation:
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for community support:
- Discourse Solved (Accepted answer plugin)
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Question Answer Plugin
- note: this one can be used in place of or together alongside Solved
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for fun and general usefulness:
I use several others, but these stand out as my favorites for the moment. 