How do I start the Mage faction quest line?
Solution 1:
You can join the Mage Faction, the Scholia Arcana, in the city of Ysa, which you go to for an early part of the Main Quest.
You're looking for a building on the south-east-ish edge of the city. It's across from one of the buildings with a trainer in it (in this case, sagecrafting).
Do note that there's another Sagecrafting trainer wandering around Ysa - ignore him, you want to find the building with the stationary trainer.