waste your time with Prague, if visiting the markets is your goal. The Dresden market is great, and if you can get a reservation, Seiffen in the Ore Mountains is where all of the German Christmas crafts originate.
Similarly, if you are primarily going for the markets, I have never spent more than one day in any market - even the big ones like Strasbourg, Cologne or Berlin. Nuremberg is one of the originals, but still only takes 2-3 hours to easily see the whole thing. If you visit the small to medium markets, you could easily see 2-3 in a day if they are close together.
Weather is variable, obviously, but Salzburg was the coldest market I ever visited. Some of the best markets, pound for pound, are in northern Italy. My favorite Christmas market is still Bolzano, and the weather is usually a bit more agreeable, and the scenery is spectacular.
I need to update this post with the latest markets from this year, but here are my thoughts on the markets:
https://www.cougarboard.com/board/message.html?id=21111630