This isn't a Vampire counts army, and there are plenty of armies you can play if you want to outnumber your opponent (Orks, Tyranids, or IG) this is a semi-horde army, where you focus upon the quality of your combat, and the survival of certain units.Regardless zombies in any game have always had low I. A player who uses them makes sure he outnumbers his opponent by at least 3-1. Ask any Vampire Counts player.
I tested the Marks many times, and many times they either proved too powerful, or not powerful enough. Like this they are almost perfectly balanced. Because paying 8 points for a zombie at T5, but a 6+ save and S3 balances out - theyu don't need more power.Secondly giving mark of khorne gives not only S but fleet whilst nurgle only gains +1 toughness. Either remove fleet or give more benefits to nurgle blessed zombies or reduce points cost of nurgle marked zombies. I may have missed them but I saw no bloodletter entry in this list?
As of the Bloodletters, I did make an entry for them, but with the Hunters they proved uterly useless, so I scrapped them. May go back to them though.