It depends on how you want to play- if you like playing with the horde (tauren, orcs, blood elves, trolls, undead, and soon to be goblins): then you might like playing:
Blood elf- Paladin, Mage, Warlock, Priest, Deathknight
Undead- Rogue, Warlock, Mage, Priest, Deathknight
Tauren- Shaman, Druid, Hunter, Warrior (and soon to be paladin in cataclysm), Deathknight
Orc- Warrior, Shaman, Warlock, Hunter, Death Knight
Troll- Rogue, Mage, Priest, warrior, shaman, Death Knight
But if you like playing with the Alliance-
Dwarf- Paladin, warrior, priest, hunter
Human- Paladin, warrior, mage, warlock, priest
Gnome- rogue, mage, warlock
Night elf- druid, priest, hunter, rogue
Dreanai- Warrior, paladin, priest
Its all up to play style
There really is no answer to this as you are the only person that knows what race and class you want to be.
There is no 'BEST' class in wow. Each class has its strengths and weaknesses and can be overcome by another player who is better.
Mage
Tauren. If you do pick a Tauren, you should be a Shaman.
Class changes are not possible in World of Warcraft at this time. If you want to change your race, you can only choose from races which have your current class available. For instance, if you are a Night Elf Druid, you can only change into a Worgen, Tauren or Troll - these are races that have the Druid class available.
the T10 class gear
i would do a Troll Rogue i see those a lot
Yes, in Mists of Pandaria the Pandaren race will be added, which can become any class other than Paladins, Death Knights, Druids and Warlocks.
An orc is best race, and a protection warrior or a holy paladin are the best. If you put them together you will get a awesome combination. I have both on 80 and in arena. i barely ever get killed ever. if people like other classes and think they're better, then OK. it also matters what you're best playing as. i am an 80 warrior with lich king armor that he drops along with my paladin am very strong.
in my opinion, rogue
yes
There is really no "best race" in World of Warcraft. Sure one race might have a nice racial ability, while another race can go into limited stealth. But all in all, they are about equal. The best race is one that you enjoy playing the most.