Brand New Gladiator here, tips....go!

[Saseal]

Hmm, new to tanking also, so I also have a question -

I was under the impression (maybe I'm working with very old knowledge) that VIT was the main stat for Glad/Pali - was I wrong about this?
I'm suddenly not sure what kind of stat build I should be aiming at by lvl 50 Pali D:

[GeekMatt]

While figuring out how YOU want to build it, focus on enmity building stats because you'll need it until you're a solid ilvl. You have plenty of natural mitigation with your tank gear, but if you can't hold aggro it'll cause problems. When you get higher up, make sure you're meeting accuracy caps for whatever content you're working on without over-stacking accuracy, and otherwise keep reading up on various opinions of PLD builds.

I myself recommend having both a more DPS-oriented gearset and a mitigation-focused gearset.

[TheodoreMcIntyre]

Hmm, new to tanking also, so I also have a question -

I was under the impression (maybe I'm working with very old knowledge) that VIT was the main stat for Glad/Pali - was I wrong about this?
I'm suddenly not sure what kind of stat build I should be aiming at by lvl 50 Pali D:

You should definitely be building VIT for your PLD until you hit 50 and are at least moderately well geared. At which point you can always respec if you want. It's easy, and pretty much free, only costing some GC seals.
Personally, I have an all-vit PLD and WAR, but my WAR uses the Wave axe (CRIT/DET) and my PLD novus has its stats split between Parry and Det, with a little accuracy in there, and I don't have any trouble holding hate on most people even in all VIT gear. I also have a full i100 set of STR accessories to use in instances where I don't need all the HP.
Some of these instances include dungeon bosses and HM primals, mostly.

Really, you can split your stats any way you want between VIT and STR and still be a good tank. As long as you're not putting the points into something silly like INT, MND, or Piety.

[Rbstr]

I was under the impression (maybe I'm working with very old knowledge) that VIT was the main stat for Glad/Pali - was I wrong about this?

No, you're not wrong. It is the most important but there's a nuance to it that gets missed. Strength is also very useful for tanks as the damage they do is not insignificant and matters to their primary function of holding hate on enemies. VIT, especially when you out-gear content, can be "wasted". If you only ever lose 3k hp you don't need a 10k buffer. Strength will always add to your dps. To change the saying up a bit: You won't lose your job for carrying nothing but vit. You will, however, miss out on an opportunity to do a bit better.

When you're leveling there's no need for carrying a ton of vit around as bonus. Things just don't hit that hard and using the bonus points for strength helps you do things more quickly and hold hate against level-synced players. Make sure you've got a decent weapon and keep pretty current on the gear that carries defense and you're fine when you're leveling.
Once you hit 50, though, you open up a bunch of stuff where having the vit could really help you at lower ilevels so you should probably swap that strength to vit. If you're stepping immediately into i110ish you can easily stay 30 strength for basically anything. (And it's advantageous to use the bonus to gain strength first before swapping accessories. Accessories carry more points of vit than strength on them).

Bonus swaps are very cheap now so mess around with it.