We are from The Netherlands and cycling here is really easy. Cycle paths everywhere and people are friendly enough to help you out.
The 'knooppunten' system is the one we use a lot when cycling in weekends or so. It's kind of fun to organize your own route and you can change your mind at any 'Knooppunt'.
You should not miss the province of Drenthe, one of the most beautiful parts of The Netherlands I believe.
It's almost everywhere flat, no mountains at all! Oke, sometimes the wind can be challenging, but there are numerous villages on your route with cafes and restaurants. In the province of Limburg you find some hills, it's a nice part as well.
Don't miss out on cycling through Amsterdam, bicycles everywhere!
If you are camping and you use a GPS, download the camping poi's here: http://archiescampings.eu/by-countries/