I've used Maaco, Earl Schieb (had them out west still in 1985!), and Peach (in Georgia, naturally!) -- all cheap paint job places, but got good paint jobs. As everyone else says, do most of the prep work yourself, and strip everything you can off first. The more prep you do the more careful they'll be with it, in my experience. It's obvious you're doing it for love of the car and you made things easy for them. I figure that anyone who sprays 3-4 cars a day 5-6 days a week ought to be able to do a better job than I can! So it should be better than something an inexperienced guy can do at home.
If the old paint is good -- meaning it's sticks really good (no peeling) and isn't all cracked up all you need to do is scuff it up real good so there's no old wax or grease on it and the new paint will stick. Primer isn't necessary unless there are bare metal spots. They will spray a sealer over the old paint before putting on new though. The sealer is usually a light gray similar to primer, but it may be any color -- or even clear.