1) Where can I find this Ainkurn sword that I have heard so much about? I'm currently in the dungeon below the potion shop.
2) I often miss when trying to drink blood - what dictates a successful grab? What does putting more points into Drink Blood do?
3) Any advice on where to put my experience points? I have 55 STR, 45 Dex, and 35 Sta. I've just been stocking up points because I'm not really sure where to put them now, int/wits? They sound pretty much the same.

1) The Anhkurn Blade is found during the Vienna chapter during the Teutonic Base mission. That's still a ways off from where you are at.

2) Spend points on Wits and Feed; that will increase your chances of grabbing enemies to feed.

3) If you are playing Vanilla; the best tactic is Celerity+Fortitude+Potence then concentrate on Str/Dex as primaries. When you obtain Obfuscate, then you can become a real badass. Spend points on Cloak the Shadows + Cloak the Gathering. You can actually Stack Cloak The Gathering with Cloak of Shadows to make yourself truly invisible. When you obtain Blood Magic (Spend on Theft of Vitae). When you stumble on the Anhkurn Blade then that will actually act as your Theft of Vitae because it will absorb a target's blood on strike. You can also obtain Blood Rituals which will contain Prison of Ice... personally it's a bit OP, but if you want serious power then look there.

Enjoy!

NO! Don't raise feed! It is both expensive and stupid, because it needs you to be right next to your enemy! Try to learn all discipline books on Christoff, and pay heed to learn the one from the tremere lairs, which contains the "Theft of Vitae"! THIS is the best bloodsucking ability... It draws blood from a BIG distance, even behind walls, INSTANTANEOUSLY, the more points you 've spent on it the more blood it steals AND yields to you, and it is both rare and overpowered (only a kind of Tremere and the final boss use it). It can kill humans with one click but without giving you experience, or simply make a vampire completely empty of blood, unable to do magic, and also *crazed* (lack of blood drives many enemies nearly insane as a game mechanic, literally, which means careless, defenseless and full of openings) and trying to come near you to feed (leaving it at your mercy to chop its head with melee swings or burn it with fire weapons).

As others said, the ainkurn sword lies in the chapel at the basement of the Teutonic HQ.

And about what to raise, it is your call, boss.