I think I've finally sorted out my itinerary, and figured I'd post it in case anyone had any thoughts or recommendations, such as on the pace, locations, modes of transport, hotels, etc. Thank you!
Day 1: arrive Paris in early morning. Spend afternoon in Versailles w/ fountains (weekend). RER back to Montparnasse, sleep in Montparnasse area of Paris.
Day 2: Day in Paris. Flight to Venice in evening. Sleep in Venice.
Day 3: Day in Venice. Sleep in Venice.
Day 4: Day in Venice. Late flight to Marseille. Sleep in Marseille airport hotel.
Day 5: Short bus ride from Marseille airport to Aix. Day in Aix. Return to Marseille airport hotel to pick up bags, train from Rognac to Arles. Sleep in Arles.
Day 6: Day in Pont du Gard with brief stops in Avignon and Nimes due to bus schedules. Sleep in Arles.
Day 7: Day in Arles. Sleep in Arles.
Day 8: Day in Arles. Evening train from Arles to Nice. Sleep in Nice.
Day 9: Day in Nice. Sleep in Nice.
Day 10: Day in Nice. Early evening flight from Nice to Paris. Sleep in Paris.
Day 11: Day in Paris. Sleep in Paris.
Day 12: Depart Paris for US.