1) Continue by Train to Chartres, see the cathedral and spend the night.
2) Drive to Rennes, stopping in LeMans for a few hours. I'm not sure what you want to do in Rennes, but I'll assume you want to spend 2 or 3 nights. Otherwise you could just drive to MSM.
3) Spend the night at MSM, on the island. Note: It is not to early to think about reserving a room for August.
4) Drive to Bayeux for 2-3 nights. D-day beaches, tapestry, cathedral.
5) Drive or take the train to Paris. (I'd opt for the train.) No less than 3 nights in Paris
I don't know what your priorities are or why you selected these cities, but I think the itinerary works better if you go from Chartres right to MSM, with a late lunch in Fougeres. Then you've got 8 days to divide between Bayeux and Paris, and you've covered a lot of ground without going crazy.
If Rennes really is a priority, another option would be to continue on by train (they are fast) and leave an extra day to see Chartres as a day trip from Paris. it works very well as a day trip.