Balmung gets a bad rap for erp, but it shouldn't get in the way if you want to go with that one, the erp isn't as big as people make it out to be as no one will bug you to do it unless you ask (well, most the time, some may be weird but in that case blacklist lol)

Most severs are pretty good, i play on Jenova and we have a nice little community.
Sometimes small is better, and sometimes it's worse. I'd say do what everyone else is saying and try visiting Balmung and see what you think of the super crowded atmosphere. My first character was on the same world im pretty sure as you and it was a bit too small for my taste, but maybe you'll like it (this was over a year ago now though). Most of the benefits from each you can get with homeworld visit now.

If you wanted to try the primal or aether datacenters i'd recommend making an alt