1. not sure if there is a US/EU versions, but the game offers EU players to play on US servers (and vice versa i guess). never had any redistration/activation issues, i believe its create an account and thats it. (but i might be wrong).
2. yes on login, you just put in acc name and pw. you can have gw2 login tool to remember the login details, so you just press login and thats it.
3. there are weekly maintenance like most mmos, there are sometimes unscheduled maintenance, but thats mainly because of the huge season events been put into the game.
4. never actually paid attention to that tool, but when you quest you dont really need to be in a grp.
5. yes you can. how long it will take depends on you and what you do in the game, since almost everything gives you exp.
6. yes there is, there plenty of world events, pvp, explorations, jumping puzzles, etc etc.
7. some gear, looks realistic, other looks fantasy-like or steam-punk.