Others have given good advice here, and there is no "right" answer since it's all about personal preference. I strongly recommend at least one night in Paris to get your clock straight and rehydrate for overseas travelers. What's your hurry?. Besides, it's a great place to walk around. After landing at CDG, you can taxi/bus/train into central Paris, then book somewhere to stay near Gare Montparnasse - this is the main TGV terminal. It IS POSSIBLE to catch a train from CDG itself to Bayonnethe day you arrive, but the choices are fewer, and you risk missing a train if you have a tight connection and your flight is late or you were delayed in Customs. If I was in a hurry, I'd fly to Biarritz that day since you are in the airport already anyways.
There are many choices of hotels near Montparnasse station in many price ranges. I prefer the train into central Paris, as its the cheapest option, and you don't need to wait long. The RER-B commuter train goes from CDG (follow the Paris By Train signs), and take the Isle de France signs, not the TGV Grand Lignes signs once you head down stairs in the airport. The vending machine may not take your credit card, so have some paper euros instead, and buy a ticket for a little over 10 euros from the machine. It's about 40 minutes to Denfert-Rochereau station, depending if your train was an express or not. Once there, you are five blocks from Montparnasse. From here, walk to your hotel.......or Montparnasse if you are in a big hurry.
Book your TGV ticket to Bayonne before you go. You can combine it with a separate ticket to SJPP from there, but you don't have to. There are trains every few hours, but 10 AM is a pretty good choice. The train to Bayonne is about 4 hours, and pretty cool if you have never been on a TGV before. Once in Bayonne, you change trains to a TER train for SJPP. The station is small, and the employees sweep pilgrims onto the right platform all day long - just follow all the other people with back packs. Don't worry if that train turns out to actually be a bus, the tracks between Bayonne and SJPP are frequently out of service, but they always have a bus leaving from the parking lot as a substitute. About an hour to SJPP either way. From the station, walk into town to your accommodation. SJPP is a village, not a big city.