well there's no wrong way to kill the guy. and his sword isn't that great (the umbra sword) you should get the sword called Chrysamere instead. it's pretty simple to get.you can find it at the Cavern of Abanabi (northeast of Tel
Fyr or southwest of Wolverine Hall, Sadrith Mora). It is
somewhere in the middle of this two places. Inside the
cavern is a conjurer named Draramu Hloran. Kill her and
take the Chrysamere from her corpse.
well being a vampire, depending on what clan you belong to:
Berne clan focuses more on speed and stealth.
Aundae clan focuses on magic.
Quarra clan focuses on strength.
you don't need to feed to stay alive. you will lose life if you go out durring the day...and nobody will want to talk to you...sometimes guards will attack you.
my advice: before you become a vampire, get your character as powerful as you can (max out every skill and atribute) then you will be able to surpass normal humans by far.