Ostend or Antwerp for the stop. Then Volkel DOM Paderborn looks about right to me. In my (somewhat dated) experience the CTRs in the NL were easy to cross, usually without leaving the Dutch Mil frequency, sometimes with a handover to the local tower. Route north of Duesseldorf and Dortmund, south of Muenster. You might get a crossing of the Duesseldorf class C if necessary, but I wouldn't count on it.
Which Paderborn airport are you going to? If you stop in Belgium you don't have to worry about customs.