1. My favorite audiobook narrator has to be Barbara Rosenblat. I listened to the "Mrs. Pollifax" books by Dorothy Gilman, and Rosenblat brings all the characters (young/old, men/women, of all nationalities and personalities) vividly to life.
2. I look for narrators who make me forget that someone is reading the book out loud. I want the book (not the voice actor) to speak to me. Also, the narrator has to speak at a proper volume: I've had several books where the reader has a lowered voice (as if they're telling me a secret), which not only gets on my nerves but lulls me to sleep.
3. I have no preference for which sex the narrator is, although I agree with your answer that prefers the reader to be the same sex as the protagonist/narrator.
4. I prefer single narrators for novels, and multiple narrators for audio versions of plays. I don't care for "dramatizations" of novels (where each character is voiced by a different narrator) since it disrupts my forgetting the book is being read aloud.