Hey @Nick_Emmett, thanks for the warm welcome!
I was lucky enough to grow with the community (I started out by managing a sub community, and I was with the company long enough to help the main community double in size) so the challenges were mostly the same year after year, regardless of numbers. Sure, if an inflammatory topic cropped up it had more posts or would creep further into other topics, but I've seen that sort of thing become more of a problem in small tight-knit communities.
I think one of the most difficult challenges is change management. A large community has nooks and crannies to hit with announcements and you don't have the luxury of spreading the word as easily. When you have a major platform change or new feature, it's hard to reach everyone. Cue the influx of new questions/rants on the forum and new support tickets! We actually spent a bunch of time with the advisory board trying to match up our metrics with where the members truly wanted to see important announcements. Surprisingly, email notifications still won out! With all the ways to reach people these days, our community still wanted us to drop this kind of thing in their inbox.
Great! And thanks, again.