first deck on here would like opinions

blade of the bloodchief and captivating vampire are both really good in this deck.

staff of the death magus is not a very strong card. its at its best in this deck, but cards that only gain life don't do anything to help you win (in an aggressive deck you want to proactively pressure your opponent to end the game as soon as possible. life gain extends the game, and doesn't threaten your opponents life total). you also already have a lot of lifegain from the nighthawks.

i am a pretty big fan of vampire lacerator, and think it is probably the best 1 cmc vampire around. 4 copies of lacerator and 4 copies of pulse tracker is a great place to start. you will almost always be attacking starting turn 2, and can potentially have draws like - swamp, lacerator, swamp 2x tracker. this is very tough for most decks to deal with. back that up with removal spell for their first good creature they play and you probably win the game.

doom blade, murder, go for the throat or heros downfall are better than grisly spectacle or feast of blood. they are more versatile and don't require you to have vampires in play. festering march is bad. shrivel is better (because its so much cheaper), but mutilate is better still (because you can kill bigger stuff for cheaper). none of those should be in your deck. you don't care about 1 toughness creatures very much, and can deal with the good ones with targeted removal spells like the ones listed above.

i would also replace all of the enchantments with either more creatures or more removal spells. again, you want to pressure your opponent, and those cards can be blanks without creatures to attach them to. blood reckoning and hissing miasma are just too slow. you play them on turn 3 or 4 and hope your opponent attacks you so that you can deal them some damage. if your opponent is low on life they bide their time and don't attack until they can kill you. if they have a lot of life it does nothing to prevent them from attacking. in both cases a 2/2 creature is more effective.

Lacerators life loss is less of an issue than you might think at first. Often you will have your opponent at 10 life by turn 5 or 6 at the worst. If you played it turn one it did 10 to them and 5 to you. Since you are aggressively attacking with small vampires your opponent will often have to leave creatures back to block instead of attacking, gaining you pseudo life. They will also be forced to deal with it quickly or just die, and a dead Lacerator isn't hurting you any more. Definitely give them a try if you already have them. You won't be disappointed.

Doom blade, ultimate price  and go for the throat all have less restrictive conditions compared to feast of blood. You can always cast them. Snuff out is another sweet one, and would be free to cast most of the time.

I think you are overvaluing your own life total. Use your life like any other resource in the game. A win with 500 life is the same as a win with one life. Use that life to get an early advantage and your opponent will have a hard time catching up.