Hi!
I can't really help you with car rental as I usually travel by train or other public transportations, but I can recommend you a couple small things about Provence : don't miss the Mont Ventoux, climb all the way to the top (you can do it in your car) and you'll enjoy the trip, no matter what the weather is! You'll either have tons of snow, dive in a cloud bath, or if the weather's good, you'll see the Mont Blanc and the Mediterranean from up there.
Plus, the small roads around the mountain go through tons of little villages made of traditional architecture, you've got Sault, Caromb, and some parts of the bigger Avignon that are more than worth it.