Hyeres, la Sable dOlonne, and Paris, France

Many, many posters here have been to Paris multiple times. What kind of information did you want for Paris?

I suspect some will have been to the other areas as well.

I see this is your first post here. This forum works best if you can give us a little more information about what you want. Sights? Lodging? Transportation? When are you planning to travel? Kids? Do you have a rough plan in place already?

Hyeres has a very picturesque historic district, seemingly not often visited by Americans. Allow time to walk around there. I wandered at random into a couple of different restaurants during the 1-1/2 days I spent there and didn't find anything too exciting. If no one on the forum has specific suggestions, I'd see what TripAdvisor says since random didn't work so well for me (by French restaurant standards, I mean).

Traveling by train between Hyeres and Les Sables-d'Olonne (10-1/2 to 11 hours) means going through Paris, where you'll have to change train stations. That is totally doable but a pain, especially if you have more than minimal luggage. Therefore, I'd probably do my Paris sightseeing on the way to Les Sables, even though that means checking into Paris-area hotels twice.

ViaMichelin estimates the driving time (with no stops, getting lost, looking for parking, etc.) at 10 hours by the fastest route. That's worse than the train in my view, unless you have time to stop and smell the roses along the way in the many interesting places you'll be passing--including Montpellier, Carcassonne, Toulouse, Bordeaux and La Rochelle.

If you happen to be landing in France on May 1, be aware that you may find very limited transportation at the Nice airport, and perhaps also at the Marseille airport (haven't been to the latter). There was no public transportation running on May 1, 2017, and there were very few taxis available.

You've chosen a couple of fairly unusual places that are really far apart. I hope you've got a good bit of time to enjoy the places in between. Hyeres is a bit obscurely located to serve as a base for a bunch of day-trips. It will take about 1-1/2 hours to get to Marseille by train, and even Cassis is about an hour away. I went to Hyeres in order to day-trip to the island of Porquerolles, which is impressive by European standards for its relatively uncrowded sandy beaches but didn't impress me all that much. (If I'm going to the trouble to take a ferry to an island, I want it to be rather dramatically pretty.) I'm guessing that's not the reason for your visit, since I assume it won't be swimming weather in May. I liked Hyeres better than Porquerolles, but there are other spots that would put you closer to more of the places tourists often want to visit.

If you're flying home or onward from Paris, the trip back to that city from Les Sables will take about 4 hours by train or 4-1/2 by car (again with no stops).

"Anything not to miss." That's a tough one - everyone has different interests so the "must sees" vary. When I planned my week in Paris I read the guidebooks and then chose my itinerary based on what appealed to me (I like Impressionists, boats, and military history). Tell us more about yourself and your travelling companions and how much time you have and we can give you some suggestions. Rick has these recommendations: https://www.ricksteves.com/watch-read-listen/read/articles/paris-itinerary

There have been many posts here about hotels in Paris. Once you know which sights you plan to see you'll know which parts of the city are convenient. Do you have a price range (in Euros, please)?
Some suggestions here: https://community.ricksteves.com/travel-forum/france/paris-hotel-9c24ca47-79e7-4ea1-9580-6ce26614fed7
https://community.ricksteves.com/travel-forum/france/reasonable-hotel-in-paris