I'm a PA accepted to and entering medical school this year.
First...Do a wide search on all of the forums. There is plenty of information on this topic.
Two...To get into the door of medical school, you still need to get through the MCAT/GPA bouncer. Your experience will help, but not if your scoring 5's across the board or if your GPA is below the minimum requirement.
C...The positive side about applying to DO vs MD is that your PA grades are calculated in your science GPA for DO. MD applications only use PA courses in overall GPA (not applied to undergrad GPA).
IV....You will get no advanced credit for being a PA. You still have to take micro, histo, anatomy, physiology, some sort of physical diagnosis class, etc. A nice pat on the back and a lollipop is all you will receive.
Lastly...Having additional years as a PA makes you look like a stronger applicant, but it won't make or break your chances of being accepted. My advice is if you are really motivated and want to be a doctor then just do it now. Finish any outstanding prerequisites and apply early.