Help Planning My 2 week European Itinerary

I have never been to Nuremburg, but in my view you are not allowing enough time in Berlin, Prague or Krakow. In terms of full days, you'll have only 2 in Berlin (jetlagged arrival day is of marginal utility), 1 in Krakow and 2 in Prague. I'd consider the minimums to be 4 in Berlin (large, spread out, with many time-consuming sights), 3 in Krakow (with Auschwitz) and 3 in Prague.

The fastest train from Krakow to Prague takes 6-1/2 hours. I haven't checked flights, but by the time you get to and from the airports and allow 2 hours for security procedures, flying won't save you much time.

This is helpful. Thank you. I'm pretty set on Nuremberg and Krakow, which would mean dropping Prague. Have you been? Am I making a mistake?

Just flew to England from Prague a few days ago. Spent 8 nights in Prague. Beautiful city. But Europe is full of beautiful cities. You can't see them all on one trip (or 10 trips). The best you can do is make each trip special, and for me that means being smart about the logistics. Too much time spent moving around and too little time actually sightseeing at my chosen destinations makes for a less-enjoyable trip, and probably a more costly one because of the transportation expenses.

Of the places on your list, I think Krakow is the most awkward to get to, so if it's a must, I'd try to allow sufficient time there so I wouldn't feel I needed to return immediately to cover all that I missed. That's the way I think about my itineraries. Other people are delighted to keep returning to the same city each year for a few days. I can't stop thinking about all the places I haven't even been to once.

Pretty ambitious itinerary, but it's a way to see the highlights and plan a return trip later. You will spend a lot of time traveling. It's 4 hours flight time from either Berlin or Nuremberg to Krakow (always through Warsaw). There is a train, also 4 hours, from Berlin to Prague, and a bus to/from Nuremberg, also 4 hours. There used to be a train with 2 transfers, but I don't see it anymore.
Berlin is huge so unless you plan to stick to one area, you will spend time on the subway and bus. If you stay in Mitte many of the top tier museums are within two or three subway stops or a few minutes by bus. There is a ICE Sprinter from Berlin to Nuremberg that makes the trip in just over 3 hours. It's a one hour flight, but with travel to the airport and security check time, the train is faster.
It's actually not a bad time to go. I used to live in Nuremberg and still go back and visit, always in December. It is cold, but the Christmas markets are all open. The one in Nuremberg is one of the largest and well known. If you stay in the old city or by the main train station most everything is walkable except the old nazi rally grounds and document center (Tram 8 from the train station to the last stop).

Personally, I would skip Prague and add a day to the other cities, then fly from Krakow to London.

Thank you so much. I think omitting one of these stops (perhaps 2 of them) is the right idea, so I can really enjoy the trip. I get to travel to Europe for two weeks every other year and always feel the need to do too much. In 2016 I did 5 stops and wish it had been 3 or 4. This discussion is a good reminder of that.

Thank you all for your feedback!

Too many stops. All the large European cities are worthy of 4 days minimum.