Champagne region itinerary

Besides Champagne, what other parts of northern France do you want to visit?
Personally, I would not want to spend more than 4-5 nights in Champagne, split between Reims and Troyes (you can take the bus from Reims to Troyes, it's only 1.5 hours). You could add Epernay if you have a strong interest in Champagne wines.

The easiest "natural" add-on to Champagne would be Alsace, perhaps with a stop in Metz along the way, but it is also feasible to reach Lille from Reims (often through Paris, but that's not a big deal given how close Paris Est (for Reims) and Paris Nord (for Lille) stations are to each other).

Thank you for your reply. In addition to the Champagne region, we would like to go to Normandy and Mount St Michel. Return back to Paris from there to catch our return flight to the states. We will be depending on trains and buses.

OK!
Normandy and Champagne are in opposite directions: going from one to the other takes most of the day and involves crossing Paris.

Since you fly out of Paris, you need to stay in/near Paris for your last night: are you open to flip your trip around and finish it with the 6 nights in Paris?
It removes the need for an additional night in Paris at the end. If you do so, I would start with Champagne (easy to reach from CDG airport), then Normandy, then Paris.

If not, my suggested order is:
Paris - Normandy - Mont Saint Michel - Champagne - CDG airport hotel - home

I would spend 3 nights around the D-day beaches (assuming that's your main draw to Normandy), Bayeux being a good base (direct trains from Paris, and plenty of yours).

Then 1 night at Mont Saint Michel (train from Bayeux to Pontorson, then bus or cab).

Then back to Paris and onwards to Troyes for 2 nights - a beautiful, lesser-visited medieval city.
And finally on to Reims by bus, for 2 nights.

You can take a fast train from Champagne-Ardenne TGV station to CDG airport at the end of the last day, and spend your last night there.

Thanks to all those who responded to my inquiry regarding an itinerary in France to include Paris and Champagne.
I have now included Alsace. So, my plans are 7 nights in Paris, 3 nights in Riems, 5 nights in Strasbourg and the last night at CDG. We may rent a car for a day in Reims and in one day in Strasbourg. Otherwise, we will be using trains and local transportation.
Again, many thanks!