driving to Bayeux and Mont St. Michel from Paris

There is a way to limit driving if you reverse the order of the trip. Specifically, from Orly you can take a cab to Massy TGV train station, a quick ride away, and take the train to Rennes. They are quite frequent: you'll be in Rennes by 9.30PM. Overnight in Rennes, pick up a car in the morning, visit Mont Saint Michel, continue to Bayeux. Visit the beaches, drive to Caen, drop car there, then train to Paris. And visit Versailles from Paris rather than swap locations.

If you'd rather drive, your original plan can work (mind that you'll drive for 10-11 hours in three days NOT counting D-day beach touring), but I'd still suggest you don't sleep near Versailles and head straight to Paris instead. The best route from Mont Saint Michel to Paris goes via Fougères, Ernée, Laval, then highway to Paris. About five hours with breaks. Don't be tempted to keep going on the toll free N12 from Fougères all the way to Paris, it is endless and has some nasty traffic choke points.

Mont St Michel is at it’s best between 5pm and 11am the next day, when the hordes of tourists and tour busses are mostly gone. I highly recommend spending the night on Mt St Michel. It’s magical if you do it this way.