Paris - Bayeux -Brittney - Saumur *Paris

As you say you like to move around a lot, this may work OK for you. It's not too extreme, though I think it would leave me hungering for more time in each place. For example, if I had only half a day for MSM I'd just as well skip it. OTOH, I salute you for choosing some of the less heavily touristed places in France.

Remember that when you stay 2 nights in a destination, that gives you one full day to enjoy and explore. The day of arrival and day of departure are largely taken up by unpacking and packing, checking in and out, navigating to your next lodging.

Half day for MSM is fine by car. Pedestrian crowding can slow down your actual visit, however. Clearly you have been to enough old cities that you don’t need to soak-in the bustling medieval main street at MSM! I wouldn’t bother to stay right in Dinan, but that’s okay. Remember that many old-towns like Dinan are closely surrounded by banal modern low-rise cities. We went to a lot of public gardens which would be lovely in June, but some roads are very rural (if well-paved) and even with GPS any excursion takes a long time. Megalithic stones take a lot of driving, too.

Thanks...definitely only 2 nights in Bayeux and plan to leave early morning to get to MSM and leave early. In Brittney will be driving around for day trips relaxing late afternoon and evenings at our base location. And it takes us minutes checking in and out these days. I have to do more research and may reconsider Saumur and tack on more days Brittney and Paris. I wanted to
go to the Loire Valley...maybe another trip. The Chateaus there look amazing!

I changed my itinerary....I think it makes more sense

JFK Paris 3 nights
Train to Bayeux - rent a car - 2 nights
St Malo 1 night off to MSM the next morning - Just spending the morning there.
Dinan 2 nights
Vannes 4 nights
Return car - Train to Paris 3 nights

You'll pass quite close to Mont-St-Michel on your way to St-Malo then have to double back. And Dinan is not much more than a 30-minute drive from St.-Malo, according to ViaMichelin. I'd do something different with my accommodations during that part of the trip. Full disclosure: St-Malo was too touristy for me to want to spend more than a few hours in the historic center. I know other people have had a different reaction and enjoyed multiple days there.