It depends on who "your community" is - if they're people who can set up their own instance, and care about decentralisation - congrats, there are already loads

It depends on who "your community" is - if they're people who can set up their own instance, and care about decentralisation - congrats, there are already loads of them on the Fediverse, in terms of users and instances. C) solved. If your community is "people I'm interested in talking to" then they don't need A) or B, and there are so many of those on the Fediverse that congrats, C) is solved. The fact of the matter is the Fediverse (and even just Mastodon) is that 1) is not the current reality (plenty of medium and small-ish instances), and 2) does not have to be, and indeed is not the reality, and even if it were, A and C still need not apply. I sometimes fear people jump into the Fedi but, understandably, aren't versed on how discoverability works, thinks there's no-one interesting there, and leaves. Whether setting up your own instance or using a tiny existing one, you can browse the user directories and posts from other, larger instances, and find interesting souls to connect with, without having to make an account there. Most importantly one can search tags used in posts and profiles which relate to your interests. Any good / mature client (or the web UI) lets you search for tags and pin them as their own timelines - so a rolling conversation about your fav topics, across all instances that you federate with.