Nice idea for undead, great race and nice combo`s for them. For 5th unit you have more choice then Bone dragons, sinisters/adept of darknes/evil genius/dread eye/ritualist all nice and new undead units
Good thing steam armor works for almost all of them, and it`s among best armor item in game. Also undead have great item sets, Moro dark is best companion pick, but for warrior new kotor is also good pick. So have fun with your playthrough