It's magic damage, so would scale off of spell crit (as it costs magicka and is a spell) since it's magic damage you'll want points in thumatauge, and spell penetration.
Since its magic damage it's spell crit, although I'm not sure how it works since it's a flat value of damage recieved = damage dealt.
How much health are you planning to have? Can't see it working that we'll without 40k+ health.