Corrected entry: Xander looks for Angel's help to save Buffy from the Master, yet, no human knew where Angel lived, so how would Xander know where Angel lived?
Corrected entry: The Master is described as a vampire, albeit a very old one, but when staked, his skeleton remains so that it can be used in the next series. Why doesn't it turn to dust like every other vampire?
Correction: The Master is the oldest vampire known - thats exactly why. He's so old, his body is too powerful to simply collapse into dust with the poke of a piece of wood. This was actually stated in one episode of Buffy, although not in such mundane terms.
Correction: Earlier in the episode Giles calls Angel on the phone. The audience is previously unaware of the info that Giles knows his phone number, so there is no reason we would know whether or not his address is also known.