Mark, I have only done a couple of trips from the Hoek to Amsterdam up the LF1 North Sea path and then onto the LF20, but here goes...
1) If you need paper maps, get them from these people
www.dezwerver.nl Their website is all in Dutch, but all you have to do is pick up the phone and a delightful lady will talk you through how to fill in the on-line sales stuff. Incredible service. I bought some
Falk maps...
Fietskaart met knooppuntennetwerk. They show all the long distance cycle paths at 1cm=500metres.
2) I went overnight from Harwich to the Hoek with Stena Lines. The Hollandica ferry is brand new, and I think that the return one, the Brittanica, will be replaced very shortly. The Hollandica has some pretty weird bike racks that you are supposed to drop your handlebars into. The slots for the bars are not that deep, and , with my bike, the brake and gear cables got in the way. Take some cable ties or cord to double up on fixing your bike.
3) It may be flat in Holland, but the wind always blows in your face....always! Chinese gales. Do not underestimate the wind when planning your progress.
4) If you have not been to Holland before, you will be dumbstruck by the cycle system...and the friendliness of the inhabitants.
Have fun.
Edit: Sorry, I just remembered that there is a network of bike-friendly and low-cost B&Bs in Holland that are run by similar enthusiasts. I don't know anything about them. Maybe our Dutch friends might help out?