Eastern France- What months?

I did the last Eastern France of the year in October, and it worked for me, weather-wise, as it was not too warm, and sometimes a bit cool.

The Chamonix/mountain part is going to vary from day to day any time of year. The day we arrived was cloudy, and no mountains were visible. The next day was clear and sunny! The cable car to the highest point was down for maintenance, so not available, though the lower portion was.

The vineyards we visited had finished harvest, possibly during harvest might hold some appeal?

I cannot answer your specific questions, but would like to point out that the days will be much longer in the spring than in the fall (would be a big deal for me). But the grape harvest is in the fall, and that might matter to you.

If you're interested in comparing possible weather conditions, I recommend the website timeanddate.com, which has actual day-by-day weather statistics going back about ten year. To me, that is far more useful than looking a single monthly average. Not finding anything for Colmar, I substituted Strasbourg. I randomly chose the month of May 2018. Unless you're immune to iffy weather, I suggest looking at a minimum of three years' worth.

Wineries are often very busy during the harvest period in late fall. Probably not a good time to get out and walk the rows of grapes. At least that's the way it is here in the Oregon vineyards.

May or Sept would be my choices for that region. Unfortunately they are no longer the shoulder season months that they used to be but they will give you the better chance of good weather and longer days combined with crowds that are at least a bit better than the June-Aug time period would.

We were in Alsace in September and it was glorious! Everything was green and the grapes were being harvested. We had a picnic on the Alsace wine route at a little road side picnic table and watched the workers pick. It was not busy with tourists around the grapes or wineries. It was a little busy in the little wine towns. Like many places, you would need to time your visit. Riquewihr can be very busy. We got there at about 9:30 am before everyone else. Perhaps it would be less busy in October and spring, but I'm pretty adverse to crowds and didn't feel too crowded.

It's a challenge to balance lower tourist load, weather, daylight hours, possibly-lower lodging costs, etc. On my one recent trip to Europe that extended into October, the shortening of the days was very noticeable to me. I now try to schedule my return home no later than the middle of September. But some other folks have no issue at all with the early nightfall or even prefer it.

Agree with acraven on short days, but it depends on the city and what you plan to do. It was a little challenging in Spain, when it was dark by 6ish, tourist venues were closed, but restaurants even tapas didn't open until about 8pm. We ended up relaxing at the hotel with a inexpensive bottle of amazing Spanish wine.
In France it was fun to see the grapes being harvested, but that is up to the year and its growing conditions. In general, I think they harvest earlier than places I've visited in the U.S., but it'd be a crap shoot.

I did the tour 4 years ago the last half of June and we enjoyed great weather. Maybe a little rain here and there, but overall sunny, warm skies. Nothing really hot that I remember.

Though weather can vary anytime in the Alps, we fortunately blessed with good weather in Chamonix.

The towns were busy, but nothing felt suffocating. You are, after all, out of the big cities.

We took the tour that started on Sept. 7th in 2014 and we had fantastic weather. Our scrapbook is linked to Rick's website if you care to look at it (Theresa and William Barr). The grapes in the vineyards were ready for harvest and we were surprised that there was still so much snow in the mountains at Chamonix (which was our favorite stop on the tour by the way). The Alps are breathtaking! This is a great tour and know that you will enjoy all of it.

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.

Be sure to take a very warm layer, hat and gloves if you go to the top of Mount Blanc

Do you mean Aiguille du Midi? The only way to the top of Mount Blanc is by climbing up the mountain.