I would most likely take the World Troller, which is coupled, and can pretty much be ridden anywhere. Don't mind the occasional thunderstorm or even a day of rain, but multiple days of bad weather would put a damper on things.
The Ardennes/Benelux sounds intriguing, but would require a bit of research because I've never been there other than Amsterdam, nor do I know much about the area, other than seeing shows about WWII battles. Probably a lot of history in the area. Maybe flying into Amsterdam, riding south and taking a train back would work. Or a loop from Paris.