Personally, I'd master Concentration first. Then master Ancient Magic to bypass enemy resistance. The skills look good to me, and I don't interfere with how you mod the combat arts. With the Torch of Light unique and the shield that gives bonus damage to fire, you don't really need to master the fire skills immediately. Platinum difficulty is where I consider the game to truly start. I generally go to level 12 in Bronze, 35 in Silver and 60 in Gold.