Suggestions for a 13 night itinerary in Eastern France

This is a great list of cities focusing on towns from Paris to Lorraine. All in all i have been to all minus Nancy and Dijon.

You don't mention if history is one of his interests as this list smacks of lots of history from Napoleon to WW2, all depends on the sort esoteric sites and museums he wants to visit.

In 1999 I first took a day trip to Chateau-Thierry on the Marne from Paris Est, last summer I did likewise, first time back since 1999, obviously the town has undergone changes. The WW1 sites pertaining to the British, French, US, and the Germans are there.

If he wants to see a "major" WW2 site but "hidden" near by Soissons, it's best having a rental car or arranging a taxi at the Soissons Tourist Office, likewise with Chateau-Thierry. That town is not only important because its role in WW1 but also in the cultural history of France, if you're into French literature at all.

Yes, Chaumont...that town is on the same train route as Troyes. I only took the train to Troyes. The refurbished and expanded Napoleon Museum , highly recommended to me by the girl in the Troyes Tourist Office, is ca. 50 mins away by bus.

I'll make a few comments on the places you've listed that I have visited. To get an idea of how many places you can see, check the train schedules at https://www.sncf-connect.com/en-en/, paying attention to frequency as well as travel time. The schedule changes in early June and I'm not certain you'll find all the June trains listed at this point. You may need to look at May instead. The schedule won't change much between May and June.

Dijon: attractive city, not tons of foreign tourists. Known for mustard. I got a kick out of the mustard vending machine I encountered.

Reims: Fab cathedral, champagne houses, and a small museum related to the signing of the WWII surrender. I didn't find it an especially pretty city (I enjoyed just walking around a lot less there than in most French cities), but the cathedral is something else. Reims often draws positive comments from others here; I'm an outlier--maybe because I have no interest in champagne.

Troyes: Cool town where I saw no other American tourists in 2017. Lots of half-timbered buildings that look tipsy. A good place to go if you want the experience of exploring a place your neighbors haven't been.

Nancy: City known as the birthplace of Art Nouveau. Lots of Art Nouveau architecture (and some Art Deco), and an important related museum. Lots of architectural eye candy.

Colmar: A really gorgeous town, but everyone knows it, so it's quite touristy. That wouldn't stop me from revisiting, because it's just that beautiful, but it certainly bugs some people--a lot. The Unterlinden Museum is excellent and has an extremely important altarpiece.

Colmar, like Strasbourg, will be an opportunity to have German-influenced Alsatian food.

Day trips from from Strasbourg to Colmar and Obernai are easy and direct, both being lovely towns, likewise with Chaumont from Troyes.

Chaumont is on my list this summer (if only I don't deviate from it) to be visited as it is connected with Napoleonic history in 1814.

I would suggest staying in Metz, it's far cheaper than Strasbourg, and logistically, going back to Germany using just regional trains in terms of reliability is more logical: Metz - Forbach/Lorraine -Saarbrücken - Frankfurt Hbf.

If you find yourself in Troyes (a delightful place), I highly recommend staying and dining at Le Champ des Oiseaux / Maison de Rhodes (two names, single hotel really). It's a former abbey dating back to the 1400s, beautifully restored. The tiny restaurant serves outstanding meals. It's one of the very best and most memorable lodging experiences of my long life.

Thank you for all of your suggestions!