3 days in Normandy

The following worked for us (although we had 6 days): (i) picked up rental car at CDG; (2) stopped at Giverney en route to Bayeux, where we based; (3) 1 full day, tour of D-Day sites; (4) 1 full day-trip to MSM. So most of your plans appear doable. I think picking up, and returning your car, at CDG will be most efficient. You'll definitely want a car to make the most of your time in Normandy. Unless spending a night at MSM is important to you (and many Forum folks recommend it highly), a single lodging decision (Bayeux, Caen, etc.) seems to make the most sense. We didn't visit Caen at all, so can't comment; but Bayeux was very manageable and having the Tapestry down the street was a convenient bonus. (If you do select Bayeux as your base, send a PM and we can offer lodging and restaurant info.) October should be perfect. Bon voyage!

With 3 days (how many nights?) I would rent the car in the outskirts of Paris and drive to Giverny. Then base in Bayeux and the next day either do an organized D-Day tour or go to the sights on your own. I would spend another day going to the WWII museum in Bayeux and see the Bayeux Tapestry. This might be possible on the day you arrive, depending on timing. If you really have 3 days (4 nights) you could go to MSM.

If you prefer to not rent a car, and if you have 3 nights, you could do something like this -
Train to Bayeux early in the day and see the WWII museum and the Tapestry. The next day do an organized WWII tour. On your departure day you could see more of Bayeux before returning to Paris. If you have 4 nights you could add a day trip to MSM from Bayeux. There is shuttle available from Hotel Churchill.

Thanks for the suggestions. We have 3 full days/2 nights, Friday through Sunday.
I want to be back near CDG for our flight departure on Monday am.

The reality is that 2 nights only gives you one full day and two partial days. There is no way you have time for all that you want to do. If you have an interest in WWII history I would take the train to Bayeux on day 1 and see the WWII museum and Bayeux Tapestry. Book a WWII tour ahead of time for day 2 (only full day). On your final partial day spend a bit more time looking around Bayeux before taking the train back to Paris. I'm not sure if you will be able to go directory the airport from Bayeux. Doing this saves you the cost of the car and hassle (no need for IDP if you aren't driving). With your limited time you will maximize your experience.

You could take a train to, rent a car and stay in Caen. Depending on what you like there are some worthwhile sights in Caen. I'd probably plan one day north and one day south. South would be the longest depending on what you want to see.

You can go to Bayeux first, by car maybe 30 minutes. I like the tapestry, I'd plan at least an hour to see it. I was there in September and it wasn't very crowded. From the looks of the ropes set up, the lines may get quite long in the high season. I walked right in and shared the tapestry with maybe 100 people (I think it's at least as long as a football field). The audio guide works well to tell the story. You can also plan a half day D-day guide from Bayeux (probably also from Caen). The town is small so it doesn't take long to look around.

From Bayeux it's about 1 1/2 hours to Mont Saint Michel. You can visit any time but I'd suggest checking the tides. I was there during the biggest tides of the year, that just means theres about an hour you can't get on or off the island because some of the road is underwater. You will want to see the Abbey on top, the ramparts and a few other sights. I liked everything about the place, even though it's very touristy on the main road.

Going north isn't too much of a lift. First go to Honfleur for a look around and lunch, then head further north toward Etretat and Fecamp. There are famous cliffs there, you can walk on the (pebble) beach, park in town, or walk along the tops of the cliffs. Good views in both towns can be had at the church that sits just north of town (both towns) at the top of the cliff. You can see the church from town and the road that gets you there. There is parking by the churches. Etretat is more touristy, Fecamp is very similar but isn't built for the tourist industry. If you like WWII, there are German defensive positions along the cliffs that are mostly filled in with dirt but not destroyed. After D-day these places were deserted and the troops pulled to use elsewhere. The cliffs are great on a sunny day and there are great sunsets, especially from the beach in Etretat.