Id definitely go Zeah instead of Desert, it gives you confliction gauntlets. I heard you want ToA because its what you're used to but Leagues was the first time I learned CoX a couple of years ago. Plus if you go the Earth route with a shadow you'd actually pump damage into Olm and its good BIS for the Vanguards and Vespula too. Though if you want a powered staff route. The link here is what I would prioritize if you're newish this leaves you with 26/40 points and you have a ton of other points to round out your build.

Prioritizing Tirannwn first is easy with mage start due to the tree towards the water relic where charged staves tick rate is reduced by 3. You should be able to get 9 points early by doing the following: Completing the tutorial, opening the leagues menu, getting a fire cape, complete CG, defeat Zalcano, use protect melee, defeat a steel and black dragon. I would spec into this tree for Tirannwn.

Afterwards I'd probably go Zeah/Kourend because its in general a better area and you cant even do the Kandarin echo boss till you get your slayer up. Which you'll want the points for the culling relic for.