Trying to spend a decent amount of time in each location - is there a more efficient order for this itinerary?
3 chateau if you arrive mid morning is really going to be pushing it. 2 in a full day is the maximum we recommend if you actually want to do more than just view the outside.
Winemakers in the Loire Valley are (as a rule) small family run businesses which are usually closed on Sunday. The winemakers see themselves as farmers and not tourist attractions - you can try plan ahead and contact a load of winemakers to see who will be open, but with the exception of some of the more mechanised places you won't be wine tasting on a Sunday. You will also have to ensure that they speak english, something not many winemakers do.
Thank you for your feedback Simon - besides what you mention about limiting Château stops to 2/day and the wine tasting, do you think this is a reasonable itinerary in terms of making the most efficient use of time? Do you have any recommendations for alternative activities in Loire on a Sunday (except touring more chateaux)?
How about a chateau and winery on the Saturday, and a second chateau on the sunday on your way back to Paris. If you're driving, Paris - Tours is about 3 hours, so you;ll need to leave time for the trip. If you're travelling to Tours by train it's an hour, but getting around will be slightly more complicated - but by no means impossible.
If returning to Paris on a Sunday, you should take a train, and buy your ticket well in advance. The roads to Paris jam every Sunday with weekenders returning—the same as in major US cities. The jams can be pretty bad late afternoon and evening.
I don't know for sure, but I'll bet there are wine tasting rooms in towns like Amboise or Blois or Tours that would be open on Sunday. You might not meet the winemaker but you'll taste the wine! The most efficient way to visit the chateaux is by car, but driving and wine tasting don't mix well (at least for a non-spitter like me).
An advantage of driving is stopping at Versailles on your way back to Paris, even returning the car there, instead of training into Paris Sunday and back out again Monday.
By the way, GMT refers to Britain's time zone, which is an hour behind France. So 14:30 GMT will be 15:30 in Paris -- or 14:30 in Paris will be 13:30 in London.
It may be worth noting that some things in the French country-side may be closed on Sunday, when based on US experience you would assume they would be open on Sunday. Gas stations in the more rural areas are just one example (no problem on the "freeways" but finding an open gas station on Sunday in the French rural areas can blindside you).
You might consider leaving Paris on Friday, late afternoon or early evening. Enabling you to get an early start and if you don't plan on renting a car, look at these tours. I don't think you'd be disappointed.
https://www.loire-valley-tours.com/en/
Or through the Tours tourist office.
http://booking.tours-tourism.co.uk/en/mobile/to-do?filter=c%3D33705&sorting=sa
Though they're a little pricey, you'll cover some great Chateaus.
Edit.
There's a left luggage nannybags by the Versailles RER station.
Being a big fan of chateaux in general and the Loire in particular, I would say since you only have a week you should head straight to the Loire region and stay there until Monday. Return to Paris on Monday, see a little of Paris on Monday evening and Tuesday morning, and then be off to CDG.
I honestly would skip Versailles unless you have your heart set on it. It is so crowded you really can't see much inside. If you do go, the "visites guidees" are well worth it, and the vast gardens & outlying grounds are not crowded but they do require a fair amount of time to get to.
The only wine tasting room I could recommend that are open on Sunday are la Cave in Amboise, which opens at 11.00am. Monmousseau in Montrichard are open Sunday but may not have an English speaker on the staff. They are part of the multinational Kingfisher and are pretty industrial in approach.
I've been to both Versailles and Chenenceau and much prefer the latter-in late afternoon in summer, it's peaceful as well as beautiful.
