Hi,
"...generally interested..." You're welcome. Obviously, the two big museums on the war are at Meaux and Perronne. Going to Perronne from Paris is not doable by train unlike Meaux. If you are staying Paris, you can as day trips see Reims and Chateau-Thierry on the Marne, the last German push. The big US monument is up on a hill, for which you need a car. The rest of the sites can be seen on foot. The monument to US 3rd Inf. Division is there, as is the nearby Anglo-French military cemetery.
Since the primary focus is northern France, I suggest you stay a few days in Arras, a city where i don't think I've ever seen any US tourists even in the centre ville. Arras was the Gen HQ for the BEF. The large British war cemetery is at the edge of town. Yes, you can walk it from the train station to track down this site, takes over an hour. At the city hall there is not only a museum pertaining to the war experience, only by guided tour, but also the tourist office with lots of material directing you to other war sites in the immediate area.
@ Wil...thanks, I'm sure you've covered more of this than I have.
The horrors of the Western Front were in the Somme and Nord Pas-de-Calais. If you want to trace the events of the Somme battle or the last German offensive in 1918 (the Kaiserschlacht), you absolutely need a car going from village to village, seeing the British cemeteries dot the countryside. To get to Vimy from Arras to see the Canadian monument you need the car. Tours are given in English and French at Vimy. Renting a car can be done at the Arras train station, ie to the left of it.