If Vandalieu is increasing his mana pool by using magic, then this is OP, he could eventually just make demon-king level undead by casting his death-attribute strengthening spell on his undead with all his mana over and over.
The living armor being a bunch of underwear is actually quite good, since there's tons of empty space in between; it's harder to hit. Plus, if each piece are all magic items, the durability should be high.