Day 1. Land in Paris after overnight flight, sleep-deprived, jetlagged. Get through airport, find hotel, check in and drop bags (if you arrive early, chances are your room won't be ready, just leave your luggage and go out. Try to enjoy as much as you can, staying awake until at least early evening.
Day 2-4. 2 full days in Paris, 1 in Versaille.
Day 5. Train to Amboise. If you get a fairly early morning train, you'll be able to drop your bags at your hotel and head out by around noon.
Day 6. Full day in Loire Valley.
Day 7. Train to Riviera. Here's the rub. Marseille is a big city, second largest in France, and it isn't really on the Riviera. The Riviera is farther east, St. Tropez, Cannes, Nice. And it is far away. And from what I can see, there are no direct train routes from Amboise. It pretty much means going back to Paris from Amboise to transfer to a train to the coast. If your heart is set on the Loire Valley and the Riviera, you'll use all of Day 7 to get there.
Day 8. 1 full day on the Riviera.
Day 9. If you can fly home from Nice or Marseille, then you'll have 1 more full day on the Riviera. If not, you'll have to use this day to get back to Paris for your flight home on Day 10. It's 3-3.5 hours by train from Marseille, add about 2 hours more from Nice. That gives you the morning in the south or the afternoon in Paris.
You are planning a trip over Easter weekend. That's likely to increase room rates. I looked at K's budget, and it's way more than I'd pay as a budget traveler. You can get a double room ensuite in a hostel in a decent, central area for €100 or less (check out hostelz.com or hostelworld.com) in Paris. €40/pp will get you a good meal with house wine, but you don't have to do that every day. Grab snacks, salads, sandwiches, wine and soft drinks at supermarkets.