We are thinking about driving parts of the castle road in beginning of Jan. Not sure of road coditions, if most castles will be open. Also have flexibility where to fly into and out of any ideas?
The official website of the Castle Road is at www.burgenstrasse.de (it has a pretty good English side). It has information about the towns on the Road and about accommodations, but I have not found specific information, including opening times, about specific castles.
The Castle Road runs from Mannheim to Prague and has 70+ castles along the length. The obvious question to start would be what section you planned to drive and where you wanted to start. As for road conditions, on this side of the Odenwald where I live, expect short daylight hours, and lots of fog in the morning. Significant snow accumulation, meaning enough snow to close a road for more than a few hours, isn't too common, but could happen. Regarding opening hours in the winter, with 70+ castles (at least by the list that I saw), you would probably have to Google each one to check. Off the top of my head, I know that Schloss Heidelberg, Schwetzingen (most under-rated Baroque palace in Europe, in my opinion) and Mannheim are open in the winter... and yes (before someone points it out), I know these are "palaces" and not "castles" (Schloss vs. Burg), but I'm not the one who designated them as part of the Burgenstraße...
According to the Schwetzingen website, www.schloss-schwetzingen.de/de/schloss-schwetzingen/Oeffnungszeiten/240269.html, access is only by tour. Winter tour times are Fr 14:00, Sa, So, Holidays 11:00, 14:00, and 15:00. . . . . . ¶ How far do you plan to go? All the way to Prague, or just to Rothenburg?