I make it 120 miles on a bike between Manchester and Hull with two large bumpy bits in the middle.I would argue that asking people do do 100 miles in a day with luggage, then a crappy night sleep on a ferry and another 60 the next day might be a bit much for a 'newer rider'. You want to make it fun, not a chore.
I'd say that is way beyond the abilities of a casual rider, loaded with luggage, to do in a single day
That would be 14-16 hours of riding time, even a decent rider would not be under 12 hrs.
In reality the Manchester Hull section is three days riding, 30 miles first day, and under 50 miles for each of the other days, followed by a night on the ferry and then a 50 mile ride between Hook of Holland to Amsterdam as the 'big' day