We had an amazing trip. Some takeaways:
1) on the main toll roads, TotalEnergy fuel stops do not take major US credit cards such as Mastercard. Other fuel stops did, but be sure to have cash on hand just in case. Tolls were easy to handle with cash.
2) Bordeaux is a lovely city worth about 2 days - add more days for exploring Cap Ferret, St. Emilion/wine country, or other day trips by car or train. In St Emilion, be aware that only certain wineries provide tours each day so plan ahead if you have a particular one you really want to see. (We happened to choose Chateau Pressac which had stunning views, a great tour, and fabulous wine for the tasting. We even met the owner.)
3) Martel is an excellent launching spot if you have a car and want to day trip the Sarlat region, Rocamadour, even as far as St. Cirq Lapopie. We stayed just outside the town in a lovely quiet airbnb and went to the Wed and Sat markets for a fun tasting and purchasing experience with the local crowd. The town itself is worth a look and the entire area is abundant in perfect small towns.
4) If you are not a city person, staying outside Paris was TOTALLY worth it (there were several on here who said not to do it). We had an airbnb an easy 10 minute walk followed by a 35 minute train ride to Paris center. Part of the deal was a ride to the airport so we wouldn't have to deal with trains and luggage. Paris was wonderful and we enjoyed every minute but we truly loved going "home" to quiet residential lodging. Totally a personal preference kind of thing of course that worked for our personalities. The extra hour on either end of the day was not a big deal. We even had a nice chat with a gentleman from the area. In a day and half in Paris, using loads of public transport, we saw the major sites Sacre Coeur, Eiffel Tower, Arc de Triomphe, Louvre exterior, wandered various neighborhoods, ate at more off the main drag restaurants. It was just the right amount of time. On public transport, we paid a bit more than needed for the Navigo Decouverte so we would not have to worry about reupping plus we were staying out in zone 5. Public transport, if you have used it in any major city was easy and at rush hour, naturally, crowded. Biggest issue was twice our cards were not accepted and we had to find a help booth at the station we were at - they would look at the card, see it was active and hand you a paper ticket to get through. Statistically 2 fails in 1.5 days isn't great - I assume like all electronic systems, it has regular glitches which is unfortunate. I would still recommend that card if you plan to go outside the inner circle of Paris for its convenience, just be aware of what to do if it doesn't work.
5) We found Peche Merle to be an amazing cave as it had both cave attributes along with drawings. We had reserved an English tour about 2 weeks in advance just in case (for early October that was more than adequate we were told after)
6) We would go back to the countryside again - at least in late September, it was quiet, peaceful, and just a joy to visit village after village, relax in nature, and otherwise just slow down as an American traveler.
Wherever you go, whenever you go - make it what you want !