The first thing to mention is that in Final Fantasy XIV, you can level up every class with a single character. There are currently 8 main classes in game: Gladiator, Pugilist, Marauder, Lancer, Archer, Conjurer, Thaumaturge, and Arcanist. FFXIV Power LevelingThese are the 8 classes which you can currently level up. Advanced classes like the Monk and Bard share levels with their parent class (Pugilist and Archer in this case) so if you have a 50 Archer, you unlock Bard just by doing a quest.
It is important to make this distinction because different leveling paths are recommended for different characters. You will have to level more than one class in FFXIV – not only do the advanced jobs require multiple classes as a prerequisite, but you can also use up to 5 select abilities from other classes when using your main class.