
Jobs take the level of the higher class, if I remember right. That is, if you are 30 lancer and unlock your dragoon, you will be level 30 dragoon. EXP gained as a lancer contributes to both lancer and dragoon, and vice versa. Dragoon will have special job abilities gained through quests (every five levels).
I can't help you with the stats for ARR, as they've changed from what I knew!
I can't help you with the stats for ARR, as they've changed from what I knew!