Sounds like you've got a start -- at least you have put some thought into this already. Seems like you've read the other thread, too.

You might think about the North Sea Cycle Route. It will give you all the countries with shores on the North Sea, including Britain. It's sort of self-guided stuff, and the part of the route I did across Northern Europe was pretty good. It enables you to head off in directions such as Brussels and Amsterdam. The route in Britain is from Scotland through to north of London, but then you can probably use some of Sustrans' other routes to get you on to Dover for the Channel crossing, or vice versa. There are ferries across the North Sea to Scotland integrate into the route.

The NS Route also gives you the option in Holland of following some of that country's other bike routes, such as the Oeverland Route, into Germany or Belgium and on to France and beyond.