I'm a pure blooded vampire and I hope I can make it a little clearer as far as your questions.
1: Some are and some aren't. Pure bloods are, and some half breeds. There are many conditions to living forever that a vampire's body has to comply with...
It would be a change of both physical and mental. For the most part it would be a physical change but it would be quite noticeable. Then the mental aspect depends on the true mental status of the mortal.