Seems like a huge trip!
If you’re going through Germany, why don't you visit the Nürburgring. It doesn't mind what day, there are always hot cars to see during summer time!
As for Belgium, though there are some exotic dealership, there aren't that many on exotics on the road, except maybe for a few places. On the 29th and 30th of July there are the 24h of Spa on the other hand. Food is easy: fries and of course lots of Belgian beer and chocolate
As for partying, you'll find plenty of it in every city and during summertime there are a lot of festivals.
As MartijnGizmo said: you have to always reserve your tickets for the Eurostar in advance!