Looking for itinerary help - Paris, but where else

Hello youwerm. QUESTIONS : What place will you be gone from ?
Are you interested in traveling in Germany ? An Express railroad train goes from Paris to Koblenz in Germany. Be at St. Goar three nights. Go on day trips, via trains, from St. Goar. One day : walk through the Medieval castle Marksburg (It is a much better castle than Burg Eltz) and visit the town Boppard on your way back to St. Goar. One day : ride on a K-D ship on the Rhine river from Bingen to St. Goar. (go that direction), and on your way to Bingen go off the train and walk through Bacharach. And, that day, it is possible to go to the Niederwald monument (on a hill at the oposite side of the Rhine River) before starting the ship ride on the Rhine river. Four more days in Germany, and fly from an airport in Germany toward your home.

I don't think you'd go wrong with any of those possibilities you've thought about. But how about this: head southwest from Paris to visit Chartres and the magnificent cathedral, headquarter in Amboise or thereabouts to see the chateaux in the Loire valley, then to the Dordogne staying in Sarlat, for example, for cave art and more, on to medieval Carcasonne, Figueres in Spain and the Dali Museum and finally Barcelona. A car would be good to have until Barcelona. There, only named one museum! Happy decision-making and enjoy your trip.

How about an all-France tour since you will already be there? After Normandy, head southeast or southwest, pick two stops of a week each and really immerse yourself in la France profonde. I would pick southeast, through Alsace, down to Lyon, and maybe Dordogne. But take out a map and a guidebook and have fun playing with options.

This is "a good problem to have," and a pretty open-ended question. I'd give Paris more than 5 nights, maybe a week, and then, say 3 days in Normandy, maybe one more to spend a night at Mont-St-Michel. Then south to the Loire and/or Dordogne, depending on whether your wife's castle interest runs more to Renaissance chateaux or the older fortified siege-withstanders, or both. You could finish in Bordeaux and fly home from there, or loop back to Paris via Chartres or maybe east to Burgundy for a few days of food and wine, could fly back from Lyon. That's an all-France trip, which would be fine with me but maybe not you.

I would suggest that for a May trip you try to line up your Paris accommodations as soon as you can. If you're up for renting an apartment through Homeaway, VRBO, or another website, you could have more room than in a hotel, have some meals "at home," do laundry, experience more of a real neighborhood, and maybe save a few euros. But the best apartments and hotel rooms for May are getting reserved now, at least in Paris.