Hi,
One of my friends is a second year in med school and he was a PA. He started working on it while he was still a PA student! He was in his last year and while he was doing rotations, he was taking classes at night, like Physics and Organic, that he didn't have. He graduated, worked for about a year, then was accepted to med school.
Advantages and disadvantages? I am not sure. I would think that things might come a little easier as you would already have some medical training and background. I have none, and to me, it would just seem that some things would have been easier if I had some pre-exposure to some stuff. But I don't know.
Good luck!
Billie