We'd need to know whether you intend to play on US/EU/JP data centres before we recommend a world.

Alien_Gamer is totally right by the way- race is almost completely insignificant. Go with whatever you like the look of. You should get a Fantasia (used to completely remake your character) during the MSQ if you change your mind. A tiny bit of advice though- when you make the character, spend 10 minutes or so running around so you can see it in different lighting. If you're anything like me you'll find a small fault you have to correct.

Regarding the tanks; Dark Knight isn't in the best spot and you can't unlock it until you complete the main game (it unlocks in the first expansion), so you'd have to play Warrior or Paladin to reach that point if you're determined to stick to tanks. There's no limitation on classes per character anyway so feel free to play around with everything until you find what clicks with you.

Enjoy Eorzea!