I think there's a lot of work to be done. If you want to have this as a competitive mono black file. Maybe I would think on 2 or 3 Kalitas at least (because is kind expensive) is one of the main damage sources with a
null caller mix to get zombies to sacrifice, also with this 2 you can have the Voldaren Vampire with madness of 3 black mana to be combined with 4 copies of
Heir of Falkenrath. You will have a strong flying creature using 3 mana, also using more of madness with Twins of Marauder State with a high defense and that can be sacrificed later for a good option. With
Stromkirk Condemned (That I do not personally like this creature so much), you also need to use madness spells and creatures.
If you want to use
Vampire Envoy I would put
Drana's Chosen to get Zombies also with more vampire allies.
Macabre Waltz is a great choice.
Creeping Dread I would take it as a Sidedeck, depends on who you are fighting.
I personally don't like Markov Knight because is very mana expensive just for haste and
lifelink. There are better choices and even spells like
Rush of Vitality that I would put 3 or 4 copies to save my creatures from death.
I hope you like my feedback and I wait for your comments. Have fun!