Hotel an der Nordschleife is where I usually stay too. But don't forget Bren who runs Sliders guesthouse is a forum member, if you want to support a fellow Nutzer.
As above, ferry from Dover is the cheapest option, although if you're from further north, Hull - Zeebrugge is much less driving, and an overnight ferry, so you can get plenty of sleep too, but it does cost considerably more.
Definitely, definitely, definitely visit Pistenklause and have steak on a stone. Both the steak and the chips are unbeatable. If you want the biggest pizza you're ever likely to have, Pinnochios in Adenau is where you wanna go. And be sure to make a trip to the Rewe beer supermarket too.
As said earlier in the thread, check the opening times, make sure the circuit's going to be open, but beware that can change at any moment. Try to keep on the black stuff and away from any Armco, avoid spilling fluids etc, and most importantly IMO, don't treat it like a track. Instead treat it like a one way B road, and constantly check your mirrors, Porsches, Beemers, bikes and any kind of supercar you can think of (or just a lot of 'normal' stuff with a knowledgeable driver) will catch you at a silly fast rate.