My personal choice is to avoid blasting inside the car. Being its very hard to get media out of the inside of the car. I used Aluminum Oxide to media blast the underside at a lower rate of PSI since it cuts faster. It also recovers way better than sand for re use. So you won't need to buy as much material.
For the outside of the car, I used paint stripper. Then sanded very clean with 80 grit. Then used a metal paint prep conditioner. This insures that theres no stripper residue left behind.
Many will tell you to go plastic media, which is good too. Your choice. If the body is pretty rust free, I would just strip it as I did.