Here is my opinion.

Vampire Nighthawk needs to be a 4 of, combo'd with 4x Stromkirk Captain gives you first strike deathtouch goodness and is a very cheap set of cards.

Sengir Vampire are a waste of space, there are a lot better cards.

I am assuming that you are actually building a casual deck and not really an extended deck. Mirri the Cursed is a great Vampire as well as Baron Sengir

Your 1 drop should be 4x Stromkirk Noble .

Work in some Bloodline Keeper  ^Flip for token and pump for your vampires, Vampire Nocturnus should be at least a 3 of.

Falkenrath Aristocrat need to find their way in.

Dreadbore is a great removal card if you want to stick to red and black.

Dark Impostor is a waste of a roster spot.

You need to add in red removal, list Lightning Bolt Searing Spear Pillar of Flame to counter prot black like Knight of Glory

Thanks heaps Scruffy.

yeh I strongly agree with most of your points. I've ordered in some Vampire Nighthawk , Stromkirk Captain , Bloodline Keeper  ^Flip and Lightning Bolt . Stromkirk Noble is an amazing card but its so expensive so I added Pulse Tracker (temporary until I can get some Nobles). Vampire Nocturnus was out of stock for now.

I changed the deck type to casual and I'll change some more when my new cards come to see what you think.

just one thing though. why the Falkenrath Aristocrat ? I would need to add humans to my deck and sacrifice creatures?