Paris-Loire-Provence

There is actually a good connection at Bordeaux that leaves at 7:49 and has the cheapest advance purchase fare, but the total travel time is 7 hours 14 minutes. The next best is with a change at Massy (just outside Paris) with a 5 hour 29 minute travel time. Use St Pierre des Corps as your station in Tours, it is just outside the city and there is a Europecar rental site at the station. Unless you are going to stay in Paris between Tours and Montpellier, be careful. Except for the route that changes at Massy, you will need to change stations in Paris from Gare Montparnasse to Gare de Lyon, which is a bit of a pain.

Thank you for the valuable information. I think we will stay couple days in Paris after Loire trip. Unless some other route can be thought of to begin with.
I thought about going directly from CDG airport down toward Loire the first day, but we arrive bit too late for a train ride down.

Which is a good town to TGV into in order to explore Provence area besides Montpellier? I would think a car rental is needed in this area, right?

I thought if the fast trains can take us to a point within about 3 hours, I would take the train rather than a flight. I chose Montpellier to get to Barcelona after our stay in Provence. But we are open to any change.

Any thoughts are appreciated :-)

Avignon might be a good spot. There are frequent nonstop (yes, nonstop) trains from Paris to Avignon that do the run in 2 hour and 40 minutes or so. There are also several direct TGV trains to Barcelona from Avignon that take 3 hours.

If you and yours can manage it, here is a good way to go.

1) Fly into Paris and go directly to the Loire valley. (Yes, hella day, but it will save you hassle later.) Settle in and do your Loire sightseeing. Car rental a good idea.

2) Then see Paris. Return the car first, in Amboise, Chartres, Versailles, or Paris.

3) Travel to Provence by super fast TGV train. Rent another car, unless you are just there for a few days.

4) Travel to Barcelona by train. If the train ride seems too long, you could break your trip in charming Collioure.

The first day is ugly, but you will minimize your transit time.

Thank you so much again.
Real time advice is so wonderful to hear. It really helps the decision making.
After all the trip is finished I will be sure to write about what we really did. Lot of the questions are asked but not too many reports on afterward to see what really happened.

Do I really need to make that much of an advanced purchase on all the TGV tickets?
Seat seem so much more limited than the JR bullet trains in Japan.

You don't "need" to buy now, but there are certain price advantages. First, if you plan on going to Tours direct from CDG, it is probably not a good idea to get the Prems fare discount tickets because they are nonrefundable and nonchangeable. Flight delays happen. I don't know your exact travel dates, but for some random days in Sept, here are some prices:
Tours-Paris, 20 euro Prems fare (nonrefundable), 51 euro normal fare
Paris-Avignon, 25 euro iDTGV 2nd cl (internet only, 17 euro change fee), 99 euro normal fare
So advance on-line purchase has some advantages. As the limited number of low fares are bought up, only higher priced fares are available, so the earlier you book, the lower the price and you have more choice of departure times with low fares.

After getting inspired by the videos, you'll find all of Rick's how-to practical advice in the guidebooks. Most of the train connections from Tours to Montpelier or Provence are via Paris; remember that you also have to connect train stations in Paris by taxi or public transport.

Sometimes, you can get from Tours to Montpelier with one connection in Le Mans, instead, which is simpler (I see some departures around 9 a.m. but not the same schedule daily). There is also sometimes a connection from Tours to Avignon with one connection in St. Pierre des Corps (I see some afternoons but not the same schedule daily). How to Look Up Train Schedules Online gives you the DB train schedule link and tips for using it.