So from what I read this opens up some sort of dungeon that is good for starting new classes? I just hit 30 arcanist and am about to start Therm. pushing me to summoner. Should I level up to 15 here?

Do I need to do the initial quest as my lvl 30 or can I be lvl one therm and start it?

Thanks I am a little confused as to how this works and if its better to lvl and learn there or just do fates or side quests.

Thanks!