Admire you enthusiasm, but not really do-able in a day, even an overnighter would be a right slog. Not all autobahns have no speed limits and those that do only have sections of no speed limit. As for the Nurburgring, 2 overnight stops would make more sense, a day getting there, a day there and a day getting back, plus track closures are frequent in the winter months as the frost/ice never thaws.