1.If you cant wait a couple extra minutes for it to fill back up you can always leave there is no penalty for you if someone else already left group and you go before it fills back up. That said you'll likely just tick the others off since you're apparently the tank.

2.Party Leader is the one who determines whether or not to search for replacement.If youre not party leader than it isnt gonna show up for you.

3.Yes you can blacklist the players that quit. Once you finish or leave the dungeoun you can go over the contacts list and it'll bring up the parties you previously grouped with you can blacklist the quitters form there if that's your perogative.

4. Again what penalty? You dont get a penalty for leaving if someone else leaves first they do however.

I would say you're missing a bit but thast's cool though I really hope that at 51 you have your Paladin Job Stone equipped because a 51 gladiator is missing bunches of things they need to be more effective tanks.