1) YEP things like weres/vampires/basically anything can also be a mage, since that just means you're a being that studies magic, which anyone can do. Humans are just best known for it because they don't have as many other innate abilities to rely on.

2) This could definitely happen. Anything that is at least part human can become a vampire. It all sort of depends on what is becoming what.

3) This is still permadeath, though if you are a vampire or a ghost you will return to life afterwards because your soul is still there.