I suggest renting the Renaut Espace or Peugeot 807 size vehicule. I typically rent from Europcar and am happy with them. However, I have rented from
Avis and Hertz as well and they were all nice. Hertz tends to have the oldest cars. I would suggest avoiding National, have had poor experiences with them.
Try to find a discount code for your rental. I always rent from Europcar because I have a good code that gives unlimited milage and a discount. Many airline and hotel programs offer discount codes.
When you price a rental and state that you are a US resident, the rental price typically includes no insurance. You will need to add that into the cost or select the option when booking. Avis offers insurance up to full damage wavier where you would owe zero in the event of an accident or theft. Europcar and Hertz allow you to reduce the deductable but not to zero. Your credit card may also include insurance for damage to the rental but not liability. Just read the terms carefully on your credit card insurance as there are some exclusions.
A tip on MSM, arrive as early as possible as it gets crowded as the day goes on.
Interstates are very well maintained in France and allow speeds up to 130 km/h . They are toll so have change ready if possible. For some toll interstates you pull a ticket and pay when you exit but I think most of the ones towards Normandy have the change basket.
Traffic forcasts are as follows:
Dec 22, 23 and 24 leaving Paris: Red or Orange = very very dense traffic and traffic jams.
Dec 30 leaving Paris : Orange = very very dense traffic and traffic jams.
Jan 1st Returning to Paris : Orange = very very dense traffic and traffic jams.
Traffic forcast for all other dates is green so no heavy traffic expected.
If you are uncomfortable driving in Paris, I suggest a rental pick up at Porte Maillot. That is right on the edge of Paris proper (not the burbs) and is a straight shot to the interstate towards Normandy.
As the prior poster suggested, an international drivers license would be helpful if you encounter the police ( something that has never happened to me). I personally have never had a rental agency ask for one.
France now had stationary radar detectors on the side of the road. I suggest obeying the speed limits very strictly to avoid a fine.