Adeptus Mechanicus Corpuscarii Electro-Priest as a PC? Want to through lighting without using the warp? Would this make a useful/viable PC? What powers/attributes would it have?

Ahm... well... Luminous Blast?

Yeah, take the Luminen talent tree and house-rule some more talents and/or augmentations to bolster it.

Or give them Electrostatic Gauntlets as exotic weapon.