Sorry I have not read this part of the site lately so have been absent on this discussion.
1. As to the train from CDG to Le Mans. Great way to travel for Americans if you've never done it, you have to go somewhere on one of these fast (186mph) suckers. It's a trip!!!
2. Obviously, you pack very light regarding gear to take with you, sleeping bag, small tent, soap, towel, clothes, hat, raingear, flashlight, tuneable radio (frequencies are different in Europe so our digitals won't work over there), put it all in a ice chest, seal it and put it in checked baggage at the airport(make sure it has wheels THAT WORK), etc. Ask me about my first time if you don't know the history on that trip. The TGV is located in the bottom floor of Terminal 2 in the center of the huge building. Go to their website to see the terminal layout, Google search.
3. When you get to Le Mans go to a store (Gilles could recommend one) to purchase what you don't bring with you because you will need more than you can bring (food and drink) unless you are prepared to wilderness camp. You could eat all meals at the circuit's vendor's but that could get expensive.
4. General admission ticket at the gate gets you inside so buy it then, in Euro's. If you bring a car (I did not drive in Europe) you will need a camping permit so buy it in advance from ACO as has already be mentioned. Grandstand tickets are hard to come by but you can monitor this site to see who might be selling tickets and strike a deal to pick them up at the circuit or make other arrangements. You don't really need them but they are very nice for the begining and ending of the race. I did it this year and am very happy I did. This is a rare event in your lifetime so a little splurge for this was well worth it for me.
4. Be prepared to walk your butt off. You walk everywhere, as most Europeans do, rather than ride in big SUV's everywhere like we do.
5. Sleep before you go and be well rested when you get there. There is so much to see and do, visit with folks, walk the circuit, etc. etc. I have been fortunate to have gone this year and last year and never thought I would have ever gone. Both times were trips of a lifetime for me. I was is awe of the whole scene. Racing at full speed at 3 AM is something we have never seen in the US and must be experienced. I just can't tell you the feeling of that sight and sound (the Corvettes must be heard) at that time of the morning.
This is the start of a great adventure. So enjoy every thought, every spoken word about going, every email, every website for information, every planning session, and take lots of pictures. If you have any other questions, please let me know. If I didn't do it, I may at least have an opinion.