We went from Dover to Dunkirk (Dunkerke, Dunquerke??? about 3 ways of spelling it),
Even if you don't want to go on the track there is plenty to do there from going up to the GP circuit, to heading to the corner where everyone crashes on youtube and watching some action unfold (never can remember the name).
Plan your petrol stops if you can, remember that in most service stations along the way you have to go in and pay for your fuel first (no idea why).
Good attempts on the french spelling for Dunkirk, for future reference, it's: Dunkerque
As for things to do around the track, as you said GP circuit, and always fun to go to "that" corner! Also you have Koln and Luxembourg a mere hour drive away.
As for paying in petrol stations before you buy, it's to stop people stealing fuel as it probably usually occurs in that area.