Do I have to go to one of the major train stations to pick up the hi-speed train to Reims, to pick up the Eastern France tour? Or can I pick up at the airport? Thank you.
I arbitrarily chose a date for the trip; the main page is http://en.voyages-sncf.com/en/ where you can construct your own itinerary.
The big link suggests the route from CdG TGV station goes to Champagne Ardenne connecting to an 8-km local train to Reims.
I took this tour a couple years ago. I booked my train on raileurope.com. Sometimes it's cheaper on local rail sights.
Anyhow, I landed at CDG and the train station is right at the airport. You might have to walk to the station from your terminal. I was in a different terminal and I'd say it was a 10-15 min walk. There may be busses as well but I just walked.
I don't know how booked in advance that kind of train gets. I booked a later train just to allow for flight delays. I ended up on time and waiting 2-3 hours, but it was the price for peace of mind.
I took the train from Paris to Reims last year, with a transfer at Champagne-Ardenne. The transfer was so easy, the local train was waiting when the Paris train pulled in, just walked across the platform and got on.