outside Paris 3 days mid-October

Perfect amount of time for the Loire Valley. Take the train to Tours. Rent a car. Visit a few chateaux.

Under similar circumstances, but we had 5 nights to cover, we went to Normandy. You could train to Bayeux, see the Tapestry, take an Overlord tour of the Beaches on the full day, maybe take a van trip to Mont St. Michel on the other full day and then train back to Paris. the hotel Churchill is a lovely place to stay near the Tapestry and pick up point for the tours and they run a van tour to Mont St. Michel (which fills up of course, so if you do this reserve ahead. I think they take anyone, not just those at their own hotel).

I second everything that janet said,the Normandy tour pickup point is 300 feet from the entrance to the Hotel Churchill and a great place to stay.
Mike

So you have the nights of Oct. 14, 15, and 16 to cover, i.e. your jet-lag day plus two full sightseeing days, before going into Paris. That's enough time for Bayeux and beaches, as suggested above, if you feel up to driving there after your overnight flight. Or you could take a TGV direct from CDG to St-Pierre des Corps, outside Tours, takes a couple of hours, then rent the car to explore the Loire. Or another TGV to Reims (less than an hour, with a train change), then explore Champagne (the area and the drink). Or the same TGV to Strasbourg (2 1/2 hours, no change) and explore Alsace.

EDIT -- Be sure you allow plenty of time between scheduled landing and TGV departure, I'd say at least 3 hours. Your flight may be delayed, you may have to wait for checked bags, and/or you may have a long line at border control. Walk-up train fares will be very expensive, the cheaper advance fares are non-refundable if you miss it.

All these side trips keep you out of Paris till your hotel or apartment is ready. Those involving trains look pretty easy for that first day, especially if you spend the first night near the station. I've driven from Bayeux to CDG in a few hours, it's quite doable but I'd hesitate to drive that much after my typical near-sleepless flight.

Trains will get you back into Paris easily (not via CDG) from all those cities. If you opt for Normandy, consider returning the car at Caen or Rouen and training in, or maybe all the way in to La Defense or Porte Maillot west of the center. Depends on where your rental company has branches.

Yours is a good problem to have -- extra time in France! :-)

Thank you , everyone. Several great ideas. As usual this forum offers great help.
We were able to find a flat in Paris beginning oct 14. Will likely do the train to Strasbourg for 2-day visit mid trip. Susan

If you're going to Strasbourg, another option is to stop in Nancy on the way back to Paris. Nancy is an undiscovered gem, and if you're interested in glassware or Art Nouveau, it's a must. And Place Stanislas, the main square, is lovely by day and even more gorgeous at night.