I had a lovely tour, did not encounter a single drop of rain for a week, and thoroughly enjoyed the whole experience. It is so convenient, from here in Northumberland, to ride to the boat in Newcastle and arrive next morning ready to tour, that we will be doing it again - and perhaps regularly.
My main (only?) significant route-planning 'mistake' was that on leaving the ferry terminal I set out to locate the nearest numbered waypoint, to begin my navigation northwards. 93, or 96 I think. This led me into town - and got me lost, within minutes of beginning. Quite discouraging! At the end of my tour, back at the ferry with time to spare, I rehearsed it again and found that (to head north, which was my plan) one should turn hard left on exiting the terminal, and simply follow the south bank of the canal to the ferry across to Velsen Nord. Easy! I know for next time.
I rode each day with a simple list of numbered node points, and rarely consulted the map except in the evenings, when planning the next day's route.
I had joined the Vrienden op de Fiets, but this did not work for me. Maybe I was unlucky. I made three calls from home, in advance of my trip, and always began by explaining that I was a member calling from England and asked if they could speak English please. Three times I was met with a brusque 'No' and the phone went down! Maybe I just sounded dodgy... My fourth call did yield a booking for my first night, but as I left the boat that morning I picked up a message from the host saying "You cannot stay tonight. I wish you good luck for another stay." Not great. I reverted to B&Bs, and won't be trying the Vrienden again. Which is a shame, because I liked the idea...
Anyway - my week was a delight, and I thank those who gave advice and encouragement here in the forum.