I see it is a bit complicated to get information on the train connection from CDG terminal 1 to Orleans. SNCF website offers connection through Lille!
I do not need to get on TGV. Ordinary train is OK. Can I get just one ticket for RER and train to Orleans?
Yes you can take the RER B from CDG Aeroport 1 train station to Paris, Saint-Michel Notre Dame, transfer to RER C to Gare d'Austerlitz, where you can take an Intercities train to Orleans.
You can purchase both train tickets from CDG Airport 1 train station ticket office.