Hoi
Just returned from a trip to the Low Countries. Good fun and pretty straightforward.
If you route via Dover you can expect a route either via KOK or direct EBOS. Will depend a bit on whether the mil areas are active or not. Ostend Approach or Koksijde can inform you.
FIS in Holland can be obtained from Dutch Mil 132.35 who are pretty helpful.
Go to AMS if you are feeling flush but Lelystad is pretty wel placed and apparently taxiride is affordable or you can catch the train.
The Jepp chart is OK. Airspace is pretty straightforward in Holland.
Mode C is compulsory above 1200ft and no exceptions are allowed.
Make sure you get the appropriate plates for the airfield you are going into as there can be some routing to follow and a prepared man counts for 2.
Hilversum is nice but has 'only' grass RWYs some of which are not very long. Not a problem in itself but I remember from another thread you are looking to go 6 up in a PA32 in which case a long tarmac job may be a better bet.
Have fun.
FD