Zombie decks from this set are going to be so awesome. The cards have so much synergy with one another it becomes really difficult to pick your strategy!
I agree with robort about the
Stitchwing Skaab, I run it in my zombie deck and it's very effective. It's nice to have a variety of flyers to give your opponents more to worry about with blocking. I also think you're going to need more discard triggers to get your madness cost for
Gisa's Bidding and the others with madness. I also think he might be a good replacement for
Rottenheart Ghoul, but that's personal preference.
Compelling Deterrence is also a good card that you suggested to me once.
I personally like
Diregraf Colossus very well. He is awesome to bring back from the graveyard after you've filled it with lots of zombies. He also generates tokens for you which fits into your theme! All in all a great deck that's going to be fun to play!