How do I stats and do I need to cross class?

[MistakeNot]

Which stat (VIT or STR) you should focus on as a tank depends on who you are talking to. With the upcoming changes announced for 3.2 it seems like VIT will be the best choice however.
At the moment you want "enough" VIT to survive and then STR for extra damage. What constitutes "enough" is ill-defined.

Regardless of which tank class/job you end up doing it will be wise to get gladiator up to level 22 at least for the Provoke ability. That is a very useful cross-class skill to have when tanking.

It will take a while before you can switch to Dark Knight. First you will need to hit level 50 and complete all the level 50 Story quests - and there are quite a few of those.

Marauder/Warrior might well be the best choice if your goal is to become a Dark Knight - if only because then you will not need to do any levelling of Conjurer which is a requirement for Paladin, but not for Warrior or Dark Knight.
But I really don't think it matters much if you have Marauder/Warrior or Gladiator/Paladin as your main class up until then.

[Dergensaur]

Thanks for the help. I guess I'll just do pure vitality till 30 and then experiment with the different stuff the job gives me going forward. I'll make sure to get provoke, I was just hoping I didn't have to go WAY deeper, like deep into paladin just for abilities. Oddly the players I talked to told me dark knight was a reskinned paladin, but it doesn't even use a shield, so odd. can you link to these upcoming updates if possible? I want to get decent at this game whilst leveling especially as a tank so people don't hate me.

[Lethallin]

Thanks for the help. I guess I'll just do pure vitality till 30 and then experiment with the different stuff the job gives me going forward. I'll make sure to get provoke, I was just hoping I didn't have to go WAY deeper, like deep into paladin just for abilities. Oddly the players I talked to told me dark knight was a reskinned paladin, but it doesn't even use a shield, so odd. can you link to these upcoming updates if possible? I want to get decent at this game whilst leveling especially as a tank so people don't hate me.

DRK is basically a different flavored PLD... at first. But only very early in DRK's levels (30-40). Soon enough you start getting into the mini-game of MP management while tanking, that PLD's don't focus on at all.

The specifics of the changes aren't known yet until the patch notes get released, but you're safe keeping your points allocated in Vitality. Just put them all in there, after the changes you won't have a reason to put them elsewhere. Provoke is necessary, but you can skimp out on Awareness for quite a while until you feel like getting GLD/PLD up the rest of the way.