We are going to France at the end of September/early October and want to go from Paris to the Dordogne. We are considering taking a train to Limoges from Paris, then renting a car in Limoges. Is this a fairly easy thing to do and which car rental companies which you recommend please? The main purpose in going to Limoges was to see Oradour-sur-Glane then we were planning on traveling to St.Emilion later that day, but not sure that is possible all in one day to arrive at a decent hour in St. Emilion. The other options would be to take the train from Paris to Bordeaux (skipping Oradour-sur-Glane or going from Sarlat later), renting a car there and going St. Emilion. How hard is it to drive from Bordeaux to St. Emilion? or the train from Paris straight to Brive la Gillard (skipping Oradour-sur-Glane and probably St. Emilion) and renting a car there. We have roughly a week for the Dordonge and have been there before (saw Rocamadour) but passed through quickly. I guess the last idea is to rent a car in Paris but I would definitely go outside the city to do that. Thank so much if you've made it through to the end of this lol.
I can't help with car-rental questions but would recommend using ViaMichelin.com to compare the estimated driving times for the various routes you are considering. You can get train travel times from https://www.sncf-connect.com/en-en/.
I believe road traffic around Sarlat on market days could be a bit challenging. I can't judge, because the day I went was intensely rainy, and the number of visitors was quite low; there were a lot of waiters hanging out in doorways, because they had no customers.
Limoges has a pretty historic center that's worth some wandering-around time. I was not prepared for the time required to absorb all the information at the modern visitor center (actually a museum) at Oradour-sur-Glane. I spent about 2 hours there, and I was rushing because I had to catch a bus back to Limoges. It takes a good bit of time to walk around the ruins of the town and give it the respect it deserves.
Getting from Limoges to Oradour sur Glane is easy and quick, but I don't understand why you then want to drive almost 3 hours to Saint Emilion when you will be between 1 and 2 hours drive to the Dordogne, depending on which part of the Dordogne you are going to.
Note that the trains to Limoges or Brive-la Gaillarde are not fast trains but Intercités trains which leave from Austerlitz station in Paris. Limoges and Brive are on the same train line from Paris.
At Limoges station there are all the main car rental companies, Hertz, Avis, Budget, Sixt. Please note that some rental companies may be closed at lunchtime, or on Sundays or even only open in the morning. Check the opening hours carefully.
Same remark for car rental companies in Brive-la-Gaillarde from where you could be less than 45 minutes by car from the Dordogne. (but too far south to go to Oradour s/Glane)