Avignon is a good starting point to visit Luberon area, a very beautiful area with a true flavour of Provence! It is true that the beach is not wonderful in Nice, it's pebbles only and overcrowded. All beaches are crowded on the French Riviera in August but you may like to try "Plage du Passable" in Cap Ferrat (near Nice), especially in the morning. The beaches in Villefranche (east of Nice) or Antibes - Juan les Pins (west of Nice) are sandy beaches. In any case, they're much nicer early in the morning. In the afternoons, it's nice to go to the hinterland and discover the small villages behind Nice. In Nice, the flower market is very nice.