First draft of itinerary - critique for me please??

I don't know Provence but your itinerary from Carcassonne on seems very doable to me.

Try to stay within the walls in Carcassonne. Late in the day and early the next morning the old city would be quieter and less crowded. The Hotel de la Cite and the Donjon des Remparts are 4-star places, there may be less expensive options. There are several hotels just west of the walls, a short walk. I use Google Earth to scout hotel locations, it might work for you (but avoid Les Florentines north of the walls).

Sarlat is the "big town" for the part of the Dordogne you want to see, and it's well worth a visit especially on market day (Wed or Sat I think). But I'd suggest one of the river towns. You're looking for a rental, but if you consider a B&B I'd recommend Le Petit Versailles just outside Beynac. Friendly hosts, great breakfasts, view over the valley, easy walk down to the tiny village with several good restaurants (best imho is La Petite Tonnelle).

It's nice to see an itinerary that focuses so well and covers a manageable area. Have a wonderful trip!

Thanks Dick for your feedback! I visited the websites of the B&B and the restaurant and have bookmarked both of them for reference as I start booking places…they both look amazing! And the nice thing about a B&B is the opportunity for expert guidance, which may be handy as it is our first trip to the region. As I'm doing more research, I see that Pech Merle has a 2:15 tour in English, so we might skip Albi and drive directly to Pech Merle from Carcassonne, then head back through Albi on Day 14 when we drive to Toulouse. One quick question…is Viamichelin.com fairly accurate for drive times in the Dordogne region? Or should I add extra time to their estimates? Thanks so much for your help!

In general, Via Michelin and the other online routing apps underestimate driving times. That would be especially true in an area like the Dordogne with narrow roads and many distractions. They assume you're at the speed limit the whole time and never stop to eat or use a bathroom or visit anything along the way. FWIW, we drove from Beynac to Carcassonne in about half a day as I recall, with an early start and little difficulty, but without sightseeing stops. You can really fly on the autoroutes.

Sadly, I haven't been to Pech Merle or Albi so can't advise you there. I'd love to see both. Some on this board, and other friends of mine, highly recommend Pech Merle.

Thanks Dick, I was assuming I'd need to add a little time to their estimates so it was good to have that confirmed. I've moved Albi to Day 14, on the way from the Dordogne to Toulouse. That eases Day 10's schedule and gives us time to get to Pech Merle for the tour in English, which also lets us get to our home base in the Dordogne at a more reasonable hour. And we didn't have anything on Day 14 except driving to Toulouse. I'm trying to leave driving days open to allow for serendipitous explorations:) How early should I book accommodations for the end of Sept/beginning of Oct? I know I should book cave tours as soon as possible, but should I go ahead and start booking lodging as well?

Google Earth shows about 2 1/2 hours driving from Sarlat to Albi and an hour from Albi to Toulouse, so even allowing for more time you should be OK in a long day. I'd start booking things now, or whenever you're reasonably sure about your plans. You can change later, but check cancellation policies for deadlines. Some hotel or B&B websites won't accept reservations sooner than a few months in advance, and may tell you they're "full" when they're really just not ready to handle your dates yet. The website should tell you that, or if not you can check by e mail.

A very thoughtful itinerary.

Late September should be warm, so swimming in the Gard is possible. The sun sets before 7 PM local daylight time, so keep that in mind for your Aigues-Mortes plans.

There are many towns in the are of the Rhone valley that would make a suitable base for this part of your itinerary. St Remy is popular on this board.

An overnight is the best way to appreciate Carcassonne, with a departure before the tour buses arrive the next day. If you arrive in time there is a tour of the inner keep that is worthwhile.

if you had time (but I don't think you do) I'd suggest a visit to St Cirq on the Lot near Peche Merle. If you needed an overnight stop (but I don;t think you do) I'd suggest taking it there. Do line up your reservations at Peche Merle.

Is the airport at Montpellier really better than that near Marseilles for this itinerary? Mostly asking for my own curiosity, since it wouldn't have occurred to me.

Have a marvelous time.

Yes, Deanna (and Adam). Montpelier makes a much easier and more efficient beginning for your proposed trip as it's only 40 minutes west of Arles. The airport is small and it's so quick to pick up your car and be on your way. After Arles, we stayed near Joucas, and
also in the perfect town of San Remy. You will have a wonderful trip.!

Just regarding days 6 - 8 of your itinerary . . about 10 years ago, we spent some time in that area. We had a very nice stay at Hotel Le Mas Fleurie, in the town of Vernet-les-Bains. It was very well-located for visiting the two abbeys and the nearby town of Villefranche-de-Conflent. The tiny village of Corneilla-de-Conflent, a couple of minutes away, has a Romanesque church with lots of good sculpture. The priory of Serrabonne is also worth visiting for its sculptures. Since it's been so long since we were there, I don't know if the hotel even still exists; but for a very reasonable price, we had a nice modern room, good breakfasts, and lovely, friendly service. There was a swimming pool, filled with warm water from the underground springs, set in a garden, where we enjoyed glasses of wine each evening. Highly recommended.

Many thanks to everyone for your generous advice and suggestions! I am traveling for the weekend but once I get home next week I will further explore all your recommendations, and will have more questions I'm sure! I was telling a friend tonight how grateful I am for this forum - our trip will be enriched because of all of you! Thanks again...

Your interests sound similar to ours. Here are some things we've done that are on your route.
Days 6-8: Peyrepertuse is unforgettable. Breathtaking (both for the view and the uphill hike). Definitely one of the most memorable things we've seen in France (4th trip coming up).
Day 9: We didn't stay within the walls at Carcassonne but wished we had
Day 10: We took a French-language tour at Pech Merle, so didn't understand everything that was said but the cave itself was still very worthwhile. If you decide to stay near there, St Cirq la Popie is one of our favorite villages. It's become very crowded during the day but an overnight stay gives you a quiet evening and morning. You can hardly turn a corner without seeing something picturesque.
Days 11-13: I second the recommendation for le Petit Versailles. We've stayed there twice. Mme Fleury's breakfast will knock your socks off - best breakfast I've ever had at a B&B. There are numerous chateaux nearby. Castlenaud http://www.castelnaud.com is interesting as a castle, outstanding if you want to learn more about medieval warfare. One of our favorite places to visit near Beynac is Les Jardins Suspendu de Marqueyssac http://www.marqueyssac.com. I don't know why it's not on more travel websites. Delightful gardens with several little surprises, high up above the Dordogne.
In Sarlat, the market days (Wed and Sat) are very interesting. Market stalls (great food), a fascinating people-watching scene, plus street performers day and night. We planned our upcoming trip so that we'd be there on a Saturday. If you like gardens, try to see Les Jardins du Manoir d'Eyrignac near Sarlat http://www.eyrignac.com. Good explanation about French vs English gardens and nice, varied strolling. It's not small but something about the scale and design gives it that "I could actually live here" feeling (not like some of the more monumental chateaux).
Happy anniversary. Enjoy.