We traveled to Normandy a few years ago and loved it! Great choice. Few thoughts...
Time - we spent 3 days in Normandy. Two of those days visiting Normandy WWII sites and one day in Bayeaux. I wish we had one more full day to spend at the WWII sites. We stayed in Port-en-Bessin-Huppain, which was a convenient location for visiting the sites. Bayeaux is lovely and would be a great launching point as well. The tapestry may be on tour when you visit - something to check if that is a big draw for you.
Car - highly recommend renting a car. You will be able to see much much more of the D-Day beaches/memorials then if you relied on public transportation. I don't even know how much public transportation there is around the sites along the coast. It could be difficult. Parking is very easy and convenient at all the major sites. We drove straight to Normandie from CDG - it is a lovely drive.
My family is very knowledgeable about WWII history. We ended up hiring a guide for one day. Hands down - best decision. I was skeptical since we were all very well read on Normandie, but we learned so much about the war, soldiers and some of the smaller less known sites to see. Our guide was Boy Eysbroek, he picked us up from our hotel and gave us a really impactful tour.
Some sites to keep in mind for your visit:
Longues-sur-Mer naval battery
-World War II German artillery battery
Arromanches
- Arromanches museum, 360 video, German 88 canon, Sherman tank
Gold Beach
-British 50th infantry
-artificial harbors used to bring troops and transports ashore
-only fully intact remaining German gun installation
Pegasus Bridge
-Held by British at beginning of war to weaken counter attack by Germans
Saint mère église
-John Steele of 505th Paratrooper Infantry Regiment
Utah Beach area
Point du hoc
-exhibits the Atlantic Wall, with complete bunkers and fortifications left alone since the 1945.
Omaha Beach
American cemetery
Have a terrific trip!