The Japanese are wonderfully patient and polite people.
And the other strong memory involves the vending machines to roll out cans of hot coffee just like cans of soda.
It's also worth remembering that bikes aren't generally allowed on Hokkaido trains unless you have a folder, and tandems on Hokkaido are illegal.
We used 700x28C tyres on our touring bikes. No issues really, although beware the very large step-up on the driveway crossings... if you don't have enough inflation in your tyres, you'll end up with pinch flats.
We will go back to Hokkaido and explore much more than we did last time.