AAA issues the IDP on the spot. They will take your picture for an extra fee if you don't bring passport type photos. All potential drivers should have an IDP. It's a translation of your driver license into several languages.
Please note that the credit card of the primary driver should be the one used to rent the car. We got dinged by Europcar when we returned our rental in Aix-en-Provence. My husband was the primary driver, but I paid for the rental, so we had to pay extra.
My favorite website for learning about renting cars and driving in Europe is gemut.com. They have a free downloadable brochure all about what to expect. Gemut is actually in Oregon, so you can easily call them with questions. Andy is the guy to talk to.
They specialize in Germany, Switzerland and Austria, but they are very knowledgeable about France as well. They can usually find a better price than I can online. We have rented through them for a trip driving only in France, for one driving in Belgium and the Netherlands, and for one driving in the German, Austrian, Italian, Swiss and French Alps.
I've been to Normandy twice. The 2nd time was much better than the first because we took a small group tour. We stayed in Bayeaux and saw the Tapestry -- 1066, William the Conquerer and all that. Our tour left from Bayeaux and concentrated on the American WWII sights in the area. It sounds like you will have more time than we did, so you will be able to see more. And there is lots more to see.
Not exactly in Normandy, but on the way to or from, and if you are traveling at the right time of year, you could visit Monet's Gardens in Giverny. See his paintings at Musée de l'Orangerie in Paris and then see his house and the gardens that inspired them.
And if you want to go east, I can recommend Reims and Verdun. I'm a WWI nut and have been to Verdun 3 times. Some might say that there's nothing to see in Reims except the Cathedral, which is magnificent both for its architecture and its history. Post WWI buildings dominate because the city was mostly destroyed during WWI. Of course, that's the champagne area, too, but we chose to go to the Basilica and Abbey of Saint-Remi on the way to Verdun instead.
There are so many choices. Whatever you choose, mix it with some basics of the French language and French culture and you will have a blast.