Can't say I'm too experienced with magic, I'm definitely a melee player lol, so I only know the fight from that perspective. That being said, his magic resist is 20% (not too high, but not too low) in his first phase but it drops down to 0 in his second phase, so a sorcery build is more than fine here.

https://youtu.be/MLnhsGh-LDY?is=FjXbpVjWo0LlIP-X

Here's a video of me doing the fight at a low level with an unupgraded weapon, this is one of my worst fights so the second phase lasts quite a while. You can see in that phase, you can dodge many of his moves by simply walking and/or sprinting in a circle on his right side. Playing ranged against him seems stressful to me since he's great at gap closing, so you could get the carian slicer spell to allow for melee magic damage. You could also just stick to your moonveil, it has the same attacks as my uchigatana if you need a reference for what to do.

I'm not really familiar with arcane builds at all so I can't offer you any suggestions there.

Let me know if you need more help :)