For those who may have some experience in south France, is there any helpful tips or suggestions for our trip.
Nice idea, I live in Marseille, know the area a little...

Remember that the Mediterranean South coast in France could be crowdy in the end of june/beginnng of july.
Anyway, many many things to see/do between Nice and Avignon... Pay a visit to the "vieux nice", St Tropez (crowdy place, be aware), Ste Maxime bay, all the fantastic road along the coast between St Trop' and Toulon is something to be done. Enjoy some stops on few hidden beaches with blue crystal water, or have some typical south food in some yachting old harbours along the coast (crowdy places again !).Make some stops to taste some wine (beware of cops) the Provences Rosé is world famous.
Pay a visit to le Castellet Village between toulon and Marseille (nice medievic little village) near the ex-F1 track, and on the road from the highway to the village, you'll find one the most famous rosés in the area "domaine Ott - chateau Romassan" (expensive...). Don't miss to walk a little in the "calanques de Cassis", fantastic rocky cliffs or visit by boat starting from Cassis.
Do some shopping in Aix en Provence, see the museum of history in Marseille (really splendid if you like history), or the hidden little motorbike museum in Marseille too if you fancy more (very interesting, and you'll be alone in the whole place).
The luberon National Park, and the Ste Croix Lake, the Gorges du Verdon, are to be seen if you prefer less crowdy places with fantastic open landscapes, and many medievic castel and villages everywhere.
See the most splendid old villages of South of France : les Baux de Provence and/or Vaisons la Romaine.
End by Avignon (the Palais des Papes), and Arles (the roman Arena, the Roman museum and Van gogh museum) and so on...
Welcome in France !