Nice build, I was thinking me too something similar.
To lvl up the priest, you have however to use another build, since you can't do any damage before it hits lvl4 (at least). Try to use it in tandem with 2 Black Paladins lvl3-4, 2 Skeleton Warriors Martyrs and a Necro lvl2, it works pretty well.
PS: at lvl5 a nice alternative would be to take Enlighted with the Priest instead of Conscience: it will get +3 damage per spell, one-shooting an enemy unit with 12 TOU or less per turn. Moreover in this way with the remaining APs you can also upgrade both Necros to lvl4 giving them Putrefaction (exactly 400AP), that would make the Priest even more lethal (it would kill any unit with an original TOU of 14 or less (or 11 plus Hard-boiled) in two shots! In this way it will hit not only as hard as a Flesh Golem but also twice per turn!)