I have similar questions on a December trip to Germany and Czech Republic. We're looking at at loop of roughly MUC - Regensburg - Bavarian Forest - Prague - Dresden - Leipzig (tentative) - Nuremburg - MUC and trying to decide between car, train, or combo. Right now I'm leaning toward just getting the car in Regensburg, driving to the Bavarian Forest area and back, then doing the rest by rail.

Any thoughts? Must do's or should avoid's with that?

I do have extensive experience with driving on snow, ice and mountains.