what alliance are you in? Redguard DK is most certainly a good start for your tank

I have both a stamina DK tank and a magicka DK tank. My advice is to level as a DPS to level up quicker. 2H is a good all-round skill line. Put a 1HS skill on your bar and you'll level that skill line up at the same time. Also, always have a class skill on your bar from each class skill line.

Tanking can be fun in this game, but you'll want to level a bit before you start tackling group content.

Up to you. Tanking requires more knowledge of the dungeon mechanics, so may be easier to run as a DPS until you figure out the mechanics. Nonvet dungeons don't have many mechanics, though, so you'd probably be alright. As long as you keep a taunt on your bar, and keep enemies off your group mates, you're doing your job.

The best thing, though, is to join a guild to make friends and run with them. Check out the guild recruitment section. I'd be happy to invite you to the guild I'm a part of (Fathers of Dominion), but we're a mainly AD guild. You can do cross faction grouping for dungeons, but not for PvP (and you'll want to PvP at least a little bit to unlock assault skills, plus it's fun!) If you want to reroll as AD, shoot me a message in game and I'll invite you (GT same as forum name).