The answer is the same as the maximum.
One, and that’s you (say hi!).
Your community starts with getting yourself involved. If your mind isn’t really in this, if this community doesn’t sound like a place you’ll visit on weekends, then you have no-one to start a community with. And that’s just dumb.
Worry less about the minimum number of people you need to start a community. Worry more about who you’re going to invite next.
You don’t need to launch big, you need to grow big.
Once you’re in, you can invite 10 friends. Then 10 more…
But it all starts with you. Are you in?