1) 50% of the community is english speaking, and even some russians are fluent in english, so it wont be hard for you to integrate.
2) It depends on the realm you're playing. PvE is pretty solid, but PvP is somewhat is not that good because of the class bugs which create a fotm around themselves so it would be harder for any other class in arena to play. There are major bugs in pvp however, but they're not gamebreaking.
3) As you can see on the site, X100 is the most popular server and fun realm (instant 90 pvp) is 2nd. They're both connected into a cross realm for pvp, which allows you to que against player from another realm and x1 from wowcircle as well.
4) I think faction balance is 52% alliance, 48% horde or around that number.
5) If you want PvP, go fun realm, if you want PvE, go x100. (but both are same pvpwise and pvewise)
6) Well, every class is in a way broken due to the bugs. Most broken healer for all I know is Resto druid (or could be mw monk, but both still op) and the least played healer classes are holy paladin and priest.