This game basically allow you to have every single class/job on a single character.
You will need other classes for cross class abilities and such as well.
Nice thing is if you ever decide to level scholar and summoner, the classes are shared so it is like levelling 2 classes at once.
Like i levelled my scholar from 50 to 60 and have never had to heal once, lol
Expansion is still a bit away for you as you need the 2.0 Main Storyline completed before getting access to the expansion.
Like Aska mentionned hunt and challenge log, you can run fates and leves and also may not seem like much but food that provides experience boosts.
Take your time and enjoy the game