Looking for advice on navigating CDG upon arrival and in preparation for departure

On the first leg, I think a taxi is a good idea. If change your mind you decide to take the train, I would not transfer at Chatelet les Halles but would take the RER B to Gare du Nord and change to the RER E at Magenta. If your arrival is scheduled for 10 AM, you could be if all goes well by noon. If you are committed to the 3 PM train, I think you should buy your tickets ahead of time. I once spent almost an hour at Gare St. Lazare trying to buy a ticket. It's the second busiest station in Paris and the lines can be long. If all goes well, you could have as much as 2.5 hours for lunch and I'd spend that at lunch not dealing with purchasing train tickets. I'd arrive at the train station around 25 minutes before departure time with my tickets.

For the return trip, I would either go for the metro and RER or a taxi. Le Bus Direct is great but I don't think that they vary the route for traffic conditions, the way a taxi could in adverse traffic conditions.

British Airways should arrive at Terminal 2 at Paris CDG.
Here is a 360 degree view of that terminal, from different viewpoints and different levels:
http://devaccess.itiview.com/itiview/index.php?project=1127
Click on different levels and different viewpoints and drag your mouse around the pictures.

On the dropdown menu in upper right you can also find "Paris St. Lazare".
It starts outside, but click on the red "Train Station" buttons and you'll get inside for a look around.

Finally, the website easycdg.com has LOADS of info and pics on CDG. Definitely worth a look.

I forgot to discuss the BA departure question. First, I truly believe that the circular shape and the enclosed escalators are disorienting. I find that a lot of people feel very confused when they are in CDG but actually it is not that bad. BA's departure area is in an odd spot. It is the only one on the lower level. I believe that it is Desk 9 and you have to watch for the signs and just ask at the airport information desks that are scattered throughout. Look for signs like this one: http://flight-report.com/en/report/4818/British_Airways_BA303_Paris_CDG_London_LHR Once you get to the check in desk, just follow the signs for security or ask the person working at the counter for directions. It will not be difficult.

If you're going to spend the money for metro and Le Bus Direct, and you're two people, you might as well go ahead and take a taxi. The cost difference is only 10 euros per person (and that's not even counting the cost of the metro tickets, which means the difference is even less), and you don't have to haul anything anywhere (luggage up/down stairs in the Metro).

Tix on le Bus Direct for your route are 17 euros apiece, so 35 euros. For 55 euros, you'll have a taxi from your left bank location to the airport.

(The taxi to Gare St Lazare will be 50 euros, as it's on the Right Bank.)

P.S. Look on your tickets to see which TERMINAL of Terminal 2 you're in/out of. Terminal 2 is actually about five different terminals from A to E (maybe more that I'm not thinking of).

http://www.parisaeroport.fr/en
For advice about St-Lazare, www.Parisbytrain.com

If you are going to bayeux directly from the airport and not staying in Pairs, there are trains that leave from the airport train station and you won't have to take a taxi into Paris. Go to the Sncf website and you can see the times and get more information.

There are no direct trains fromCDG to Bayeux. The best way to get to Bayeux from CDG is to go into Paris. For some reason train service from CDG to Normandy requires multiple connections and it would take about 6 hours to get to Bayeux.

we left out of CDG two days ago, what we noticed, there were reasonably long lines going through customs, so allow time. also the security ( for our flight at least) was right out at the gate area, where there was only one food outlet and toilets. we were unsure what food options would be available, once we got through customs and security. ie: we thought there might be more than there was.
we caught a taxi from the airport to taxi and return. the traffic ( in the afternoon) was very thick, so allow time for that.
hope this helps.

I prefer the RER for the return trip, because traffic can be unpredictable and it's cheaper. You are supposed to be there three hours early, so 7:20, and it's about 45 minutes from Gare du Nord or an hour by car depending on where you start. My last trip Gare du Nord was packed and I couldn't get on the first train. I took the next, less crowded, train (which splits off and doesn't go all the way to CDG) just to get away from the crowd. I think I went four or so stops (before the split) and waited for the next train to CDG. By the time it got there, the crowd on the train had dissapated quite a bit and I was able to get a seat. I really didn't lose any time because it would have been the next RER to CDG anyway.

On your way there, figure an hour to get out of the airport, even without bags (maybe a little less for a taxi) plus another hour drive to Saint Lazare. You will have plenty of time for a nice lunch. I don't know how far you would want to go for lunch. There is a small park (Park Square Louis XVI) and church about two blocks south of St. Lazare. There are some places to eat across from the front of the church that might be nicer than what's at the station.

If you're bringing a smart phone, you could get a local SIM card before you leave the airport. The kiosks should be staffed - make sure they set it up for you and it's working before you pay them. If you go downtown first, you'll be at lunch time and the phone stores will be lightly staffed and likely have slow moving lines.

On departure from CDG - be sure to allow a MINIMUM of one hour to get through passport control. Many people, including me, have had the experience of multiple planeloads of outbound passengers queuing up for one or two passport control desks. It was so challenging that I have made it a point since to fly in and out of Frankfurt, and I avoid CDG if at all possible. Go to CDG on the Google map and read the reviews for more experiences of a similar nature. Also on the last trip to France (June 2017), passengers inbound on an EU flight ALSO have to go through passport control. Good luck.

When I go to Normandy, I take the Roissy bus. You catch it right outside the terminal, it is €11 p/p, and it brings you just a few of blocks from Gare Saint-Lazare next to the Opéra Garnier. A pleasant walk along Blvd. Haussmann or Rue Auber if the weather is good. There are cafes along the way, or one right across the street from the train station (Restaurant Garnier). With two people the savings aren't as huge. But it is still €28 less total, and the bus is a fairly civilized way to travel., and I find the walk refreshing after a long flight.

You are all amazing, thank you! The Roissy bus seems like an ideal solution in & out of Paris for us. I appreciate the insight into the wait times at CDG & St Lazare...and the visual for CDG terminals were very helpful. I'm feeling a bit better about the transitions.

Any other insights are still welcome. I love the collective wisdom here :)