I have to media blast at work every now and then, even more often now that we are down to only a few workers. Just recently spent 3 days blasting a huge city garbage truck, with a big lift arm , tons of corners to try to hit, while hauling a big hose up and down a ladder, hoping it stays level in a big sand pit while crawling up and down it, being able to see what your doing for maybe a minute or so before the lens should be changed. If there were more jobs right now, or they didn't have a air supplied hood, I probably walk.
Now maybe a car on a rotissery wouldn't be quite as bad as that, but definately not a very fun job. I'd look into something else. And like others already mentioned, anything less then a huge industrial compressor, and you'd be there forever and a year trying to blast anything.
My compressor at home is a bit bigger then yours, and can't imagine how long it would take to blast a complete car with my little harbor freight blaster and the compressor I have.