Is it possible to do Mont St. Michel in a day trip from Paris? What is the best transportation? Best day of the week to travel? Would an over night trip be better? If yes, what other stops could be made on an over night trip?
I think an overnight would be better than a day trip, because a day trip would only have you there during the crowded peak hours.
I'm not sure what you have in mind with the "other stops." There are lots of great things to see in France if you have the time. You could, for instance, take a couple of days, rent a car in Bayeux or Caen, and see a bit of Normandy. But not overnight.