Hi Littlemay,
I've stayed for four years in Holland so I am familiar with the weather and way of life in Europe. But yet I cannot say that I have seen much of Europe because it takes a lifetime to explore, and in recent years I've only been to Europe for two-three week vacations, mostly to France. So I'm not that well travelled. But Europe is like a second home to me and I am completely comfortable there.
Taking trains is also a good way to travel around and you are right, it is indeed timely and efficient; just not very cheap.
It's better than being herded around (sorry Idyll!
) in a tour bus.
I don't think leave is a problem; if I had only had a short time, say one week in France, I would spend at least four days in Paris and maybe three days in the Champagne region or something like that. I'll just do less places and explore more about each place; there is no need to visit as many places as possible as if ticking off a checklist.
You're right that it may not be so wise to drive around in winter in the mountainous regions due to possible frozen roads (you would need snow tires or chains on the tyres) and also shorter daylight hours. In our own experience our family has driven all the way from Holland to Austria (8-hour drive) for a skiing trip in winter before and it was fine; but that was because we were almost like permanent residents there.
I have not been to St Moritz so I don't know; but I did hear that it is a picture-perfect place where all the rich people go for a holiday and it even has its own perfect lake. I think it might be worth going as it might be less crowded than Interlaken or Lucern; but then I could be wrong.
We went in Summer (bad time due to crowds) and stayed at a lousy two-star hotel in Interlaken so I wouldn't recommend it to you. Brunnen was just an overnight stop (but we had the best ever Swiss breakfast there!) and we stayed three nights in Interlaken and two nights in Zermatt. We also did a bit of northern Italy and touched the French Alps. Altogether we were there for about 2.5 weeks.
Let us know if you need any other advice; there are other experienced Europe travellers around (Midas, Idyll, Mrs. N, and others) and I'm sure they can help you too.