I am currently the only user. Im considering opening it up to limited users but not really having communities once i get a lot of the instances cached and indexable.
Others like @leopardboy are running on a 2GB shared just fine. I will likely move to that if i choose to keep it solo for sure, or under 100 users and no communities.
I dont have the time to really moderate others or content on the instance. So i dont think I plan to host any communities at all. I do wish you could federate/sync specific communities to your instance to make searching/subscribing easier.