I know the area well, and have made the trip many times- from Scotland though. Coming off at Calais, it's a straightforward run along the e34, then up towards Bremen, Autobahn pretty much all the way. I used to leave about 8am and get to Calais about 2ish, making a few stops along the way. Its about 400 miles give or take. Watch the Autobahns around Bremen as they are straight and wide, but have speed limits.