When i first heard the job system, i was interested in leveling the job from 1 to 50, but now i am trying to level additional classes, and it's shown me that it would be hell to have to fate grind those up, since almost all quests are gone now for me. There are job quests you'd need to do, and those scale you, along with dungeons, where you can get a hang of the new job. I wish the guildhests gave better rewards, it would be a nice place to practice with the new job/class, but it's paltry at this point.

Don't forget too that Yoshi has mentioned there will be "advanced jobs", that require more jobs or classes than now.