paris to Normandy by car

It's not confusing and it certainly is a workable plan. An alternative for your consideration would be to pick up your car at one of the outlets on the far west side of Paris near the Peripherique ring road. No airport pick up surcharge and no going out of your way.

How many days will you be in Normandy? Where will you be in Normandy when you need to go to CDG? What time does your plane leave?

In addition to what Tim said, your title says Paris to Normandy, but you question says the other direction. Will you already have a car in Normandy?

We have made this trip before and took the train to Rouen and rented a car there . We returned the car in Rouen and returned to Paris by train. Our carnet allowed us to use public transit to get to the airport. The passe navigo will have ended when we need the public transit to get back to the airport if we do the train to Rouen thing.
This time we were thinking of not taking the train, but driving to the Normandy area. We could use our transit pass on Sun. to get to the airport to rent a car at the airport and then return the car to the airport on April 28. We have hotel reservations at the airport hotel for the 28th. Flight leaves 11:40 a.m. on the 29th.
In short: Driving from cdg on Sun. to Honfleur. Spending Sun. night in Honfleur, Mon night in St. Michel and Tues. night in Dinan -driving to airport hotel on Wed. from Dinan - spend Wed. night at airport hotel and depart 11:40 a.m. Thurs. the 29th.
Hope this was not too confusing.
Thanks so very much,
Sylvia

I agree with Tim. Additionally, driving in to CDG is a piece of cake, especially from the north. The car drop lots are well-marked and convenient to the terminals as you come into the airport. Driving out, on the other hand is a bit of a pain in the tail if you're not used to it.