Marseille to Nice

A week should be plenty, and you won't need a car unless you want to drive to some of the villages in the hills above the coast. I took an express train between Marseilles and Nice so I can't speak to each stop, but you should find plenty to see and do along the way. Nice itself is worth two or three days, and you can continue east to Villefranche, Cap Ferrat, and Monaco. There are beautiful cliffside walks around Villefranche and Cap Ferrat.

The train is a bit limiting but so convenient. We're about to visit Cassis and Sanary sur Mer, after much research, for first time. We'd strongly recommend Antibes from extensive experience, with Cannes interesting for the checklist, Villefranche-sur-Mer super picturesque both in town and along the water, two days in Nice itself, and Menton for a beautiful train-reachable taste of Italy without crossing the border. 6 days is likely enough for a solid first taste ... but you could spend a month. You will be close to Arles, Avignon, Nimes, Aix [not our favorite, sorry, too many scooters and such], and many more, with a car really helpful off the coast. Monaco is a checklist experience in our view, but not at all charming or typical in the way of smaller places, and requires time to walk to interesting spots.
Enjoy!