We took this tour starting September 17th of 2017. Our weather was very nice. We had rain in Reims and Verdun and a few clouds the rest of the trip, but basically Sunshine the rest of the tour. One concern might be in Chamonix. We arrived on 9/24 which was a Sunday. It was the last day you could take the gondola over into Italy. (This was the last Sunday in September) If that's a trip you want to do, then you might want to travel earlier in the year. We had fabulous weather at Chamonix. Mount Blanc was in it's glory. Be sure to take a very warm layer, hat and gloves if you go to the top of Mount Blanc. It is VERY COLD. Also, we had a little problem with the altitude on top.. It is 12,600 feet., so it is hard to catch your breath. If you get light headed, put your head down between your knees. Drinking lots of water helps also. We had no problems with grape harvests. We toured 2 vineyards where we walked among the vines. One was in the Colmar area and one was in the Vaison-la-Romaine area. We had wine tastings in other areas, but didn't tour vineyards. It was enjoyable seeing the grapes on the vines and some areas had already been harvested.
We took a Rick Steves 7 day Paris tour preceding the Eastern France tour. We loved it. They tied together well. That tour finished on Saturday morning, which gave us all day Saturday to tour some additional sites on our own. We took the train to Reims on the Sunday that the tour started. We got there in time to visit the Surrender museum before meeting our group. Paris would be easy to tour on your own if you don't want to take the tour. Before we arrived in Paris we spent a little time in London and then took the train to Bayeaux for a D-day tour. Paris weather had rain almost every day we were there.
Most of the time on this tour we would wear long sleeves and a light jacket. The further south you go, the warmer the weather. In Vaison-la-Romaine and Aix-en-Provence we wore short sleeves. It was pretty warm (80-88 degrees). Air condoning was available every place except Chamonix (not needed). The AC in the Beaune motel was not working in our room, but other people had it.
In Reims we visited the Abbey of St Remy in addition to Our Lady of Reims cathedral which is included on your tour. We really enjoyed this tour. There were no big crowds except in Aix. It was easy to get around by foot every place that you stay.. Colmar and Chamonix were my favorites of all the places we stayed. Annecy was beautiful. The hotel in Vaison was on a hill and took some time to hike up to, but it had great views and big rooms. I'm sure you'll enjoy this tour regardless of when you go.