This is a good point for not choosing too small. I’ve made a couple of accounts, and it looks like when a servers crosses that 1,000 or 2,000 user mark you start getting much better consistency than the micro instances with only a few hundred users.
I usually find that I have to reload a few times if I’m the first person to try to subscribe to a community. That happens uncomfortably too often if the instance is small. Even then, it can take a days or possibly never to properly federate.
I’m sure these issues will be fixed, but for now, I’d like myself a small instance but not too small so as to avoid issues with consistency.