After Loire and South of France tour some changes to plan

I like it! Multiple nights in each stop; thoughtful activities. Looks good to me.

You can take a direct 30m train from the Nice Ville station to Monte Carlo. A direct train from Nice to Lyon takes 4h 30m but there aren’t many. The earliest one I see departs at 6:01a and the next one leaves at 7a and the one after that at 2:40p. There are more but those trains require a transfer.
To get from Lyon Part Dieu station to Bayeux requires a change taking 5h 15m. There are direct trains from Bayeux to Paris St Lazare station taking 2h 30m. The further out you buy your ticket the cheaper it is but it’s too soon to purchase now: https://www.sncf-connect.com/en-en/. However, it’s not too soon to buy your Eurostar tickets which you should buy after you purchase your plane ticket: https://www.eurostar.com/us-en. These tickets also go up in price the closer you get to your travel date.
I think your itinerary is fine and you are fortunate to have the time to do this.

MaryPat thank you the the train times and links.

I am on a leave from teaching this year so getting in all my travel that I have missed for the past few years.

Is there any reason that it makes sense to stay in Paris the day I arrive in France and head to Chartres the next day for the start of my tour. My plan is to land and make my way to the tour hotel for one or two extra nights as I will be spending time in Paris at the end.

Hi Wendy, what do you want to do on arrival day? One poster referred to it as a business day that I agree with. While at the airport you can purchase your metro tickets (I don’t know if the carnet is still popular where you buy ten individual tickets), withdraw euros, etc. then take the RER train from the airport to Paris which you have to do even if you’re spending your first night in Chartres.
The problem with sleeping in Paris is it’s for one night but if you’re fine with not unpacking before moving onto Chartres then sleep in a different neighborhood than where you’ll be staying when you return. This way you’ll see a bit more of Paris.
If you go from the airport to Chartres that’s two connections taking a minimum of 2h 15m. I’ve never been to Chartres but people like it and it will be more manageable than getting around Paris. I don’t know if you’ll be sleeping in the same hotel in Chartres the night before the tour begins but if you need to change hotels or rooms maybe a night in Paris on arrival day wouldn’t be so bad. If you can sleep in the same room as the night the tour begins you can unwind a bit more in Chartres and maybe meet some of the others who’ll be on your tour. You have a lot to look forward to, Wendy.