Normandy/Brittany:
With a car, you can probably do a pretty decent job of Fougeres and Vitre in one day. I didn't go inside the chateaus, but I walked around a great deal and likely didn't spend more than 3 or 4 hours in either place. My modus operandi in towns like those is to walk every street in the historic district; most travelers aren't so obsessive. Also, I was traveling by bus from Rennes, and I am not an early riser.
I highly, highly recommend a one-day van tour to the D-Day sites. It will cost about 95 euros, but it is so much more efficient that a do-it-yourself approach. If you drive around yourself you'll probably miss half of what my tour covered, and you won't necessarily understand much of what you do see. That's how I spent one full day; I took an Overlord Tour that originated in Bayeux. They do more than one tour, and there's also a two-day tour. One of the stops on my tour (US-focused) was Ste-Mere-Eglise, where most of us wolfed down a sandwich for lunch and went to the Airborne Museum. It was fine, but I thought not as professionally presented as the museums in Bayeux and Caen. It probably did have more detail about airborne activities, per se. I'm afraid the finer points of military activity are rather lost on me.
I also went to the good WW II museum on the outskirts of Bayeux. I no longer remember how much time I spent there, but it was certainly at least 2 hours and may have been 4. There's a nearby British cemetery that I didn't get to. While in Bayeux I also saw the tapestry; if you go early in the morning it won't take too long.
I spent some of my nights in Caen because it's the best public-transportation hub for a lot of the places I wanted to go. (There's also a castle.) That city has a huge Peace Museum that seems to be either really liked (by me and some others) or quite disliked (by yet others)--possibly because it is so large/overwhelming, frequently crowded, and covers more than the wartime period. I liked seeing the French take on the Cold War, but it's an 8-hour visit if you want to take it all in, and the more such places you go, the more duplication there is. I think perhaps the ticket is good for two days, but I'm not sure. It's not a cheap ticket, and it's well outside the center city, so you'll need your car of you'll be on a bus for quite a while. There is, fortunately, a place or two to get food inside the museum.
Another WW II museum I went to is a relatively new one in Falaise. It focuses on civilian life during the war, including the Resistance. I thought it was very well done. The town itself was destroyed during the war, so there's very little left to see. As an indication of how little I am interested in castles: I have no memory of there being a castle in Falaise, yet the internet tells me it has a "tremendously imposing" one! So there you have two birds to be killed with one stone. Just don't expect there to be much else to the town.
Nancy, incidentally, is sort of the mother-ship of Art Nouveau in France, and I especially like that style. It's quite a handsome city, but I don't think it's a must for you.
There are a bunch of (touristy) picturesque wine villages near Colmar, of which Ribeauville is one. You can't go wrong in that area as long as you don't expect to have the towns to yourself. Colmar is special because of its size and the wonderful museum (the Isenheim Altarpiece is a masterpiece).
All the museums I've mentioned in France and in Germany have done a good job of providing English-language explanatory material. I am dependent on that, else I'd have to spend a month in each place with a dictionary in my hand.
Apologies for all the missing diacritical marks. I'm lazy.