Can you wash your car after spray painting it?

You could, if you careful not to get it on your house or neighbors house. And you might want to have tarps all over the painting area that way it doesn't hit your lawn or driveway. However, is this car a, ahem, "clunker"? If I were you I would paint a car by yourself if you aren't a pro. I'm not a pro either, but I've seen peoples cars they have tried to paint, and it didn't turn out to well...
So, frankly i would send it to a professional auto painting shop.