1) Just sign up for XBox Silver and it'll prompt you "you are eligible for 1 month free XBL Gold" or something like that.
2) Set up in your profiles
3) Not sure, hehe
4) There are 3 (I think) different regions for XBox360. Games are normally locked for 1 or 2 regions, and cannot be played on other region(s) without any firmware mods/hacks.

Hmm I'm playing Vegas and GoW at the moment and I don't necessarily find any of em harder than the other, they're just totally different games.

Vegas can be mega annoying if you don't have surround sound cos there'll be an enemy shooting and you don't know where he's shooting from until it's too late. GoW you always know from which general direction the baddies are. Vegas for the most part your team-mates perform better than you, GoW for the most part your team-mates die first.