Flight due into CDG on Friday, Sept 7, at 7:30AM. Can we get luggage, clear passport control, & take Air France bus to PARIS MONTPARNASSE in time to catch the 11:05 TGV train to Rennes?

Yes, piece of cake.

There should be enough time if you plane arrives more or less on-time. But not a lot of time to squander.

The coach to Montparnasse can take up to an hour because of the stop at Gare de Lyon.

Also, I believe it's only once every 30 minutes, not 15 minutes like Line 2 to Etoile.

The coach is every 30 min. Perhaps I should look an hour later. Can I consider waiting to buy ticket at train station?? Hate to be pushed for time in a jet-lagged state.

I have routinely arrived at CDG at 7:30 and taken a train to Bordeaux from Montparnasse at 10:10 or 10:20 and only once missed it, and that was because of a flight delayed by an hour or more.

Should you decide to book a later train (it's better to have an hour to spare...), Montparnasse 1900, right across from the station on Blvd Montparnasse just to the left, is a lovely place for lunch. Gorgeous, vintage, Art Nouveau, interior and very good food at moderate prices.

Actually, you don't need to go into Paris at all. There is a direct TGV from CDG to Rennes departing at 10:28 and arriving at 13:27, only four minutes later than the one leaving Montparnasse at 11:05.

I think the morning train direct from CDG to Rennes only runs on Sun (unless I read the schedule wrong). My flight is Dallas to Boston with 2 hour layover and then on to CDG. Do not fly that often but guess I expect flight arrival times to be delayed.
I will hope for your luck, StCirq.
Thanks.

Yes, that shouldn't be a problem. almost 4 hours is a good amount of in-between time.

I just checked sncf.com. It lists the direct 10:28 TGV from CDG to Rennes as running every day.

Right you are TimS!! Maybe I have stared at this computer screen too long. Just booked & printed PREM tickets for CDG to Rennes.
Now if I can figure out how to do the Avignon TGV to Alassio, Italy. Posted a message on cross border train France to Italy but no takers yet.
Thanks everyone!!