Two quick questions, since everyone else seems to be asking about classes/leveling:
1. I'm planning on getting my gladiator to 30 (only 2 more levels!) and then leveling up conjuerer to unlock paladin. Is there any downside to not leveling gladiator to 50 first?
2. Do the unlocked jobs start at level 30, or 1?
3. Bonus question I just thought of: How different are jobs and their base classes? I always thought of a paladin as a more advanced gladiator, but are their roles any different? I guess what I'm getting at is, are the base classes equally as desirable as the advanced jobs?
You should unlock PLD as soon as you can, because it will give you access to several key abilities. It won't change the gameplay for you, but it adds another layer. You get a DPS stance at 30, an Intervene-like ability you can use to take damage in place of a melee or another tank at 35, your tanking stance at 40, a silence at 45, and a bubble at 50.
You'll still be level 30, since it's not the job that gets leveled up (Paladin), it's your class (Gladiator).
On the same tack, I believe that if you are an Arcanist, once you reach 50 you will be at 50 for both Summoner and Scholar as long as you've done the quests.