If you have the money and don't have the time, let them do everything.
BUT if you know what you are doing and have the time to do it....by all means I say to prime the body and paint the interior and let them finish it up.
I know how to paint...BUT my garage is far from an ideal painting booth so I will probably have my cousin paint it for me at his shop or he would probably let me use his shop to paint it myself.
I primed and painted my engine bay, I painted all my interior, I will do all my own body work,I will prime the car and prepp it for paint, I will probably paint my door jambs and inside the trunk and everything too.
then all that will be left to do is paint the exterior....saves alot of money in the long run, it all comes down to what you can do and want to do and can afford to do though