How long total will you be gone? Are you planning on seeing all the main attractions in Shanghai, Beijing, Hong Kong and Tokyo in addition to the parks?
There is so much history in Beijing I'd allow at least 5 nights there; Shanghai is amazing and the food is wonderful, but you could maybe get away with 3 days + 1 or 2 days for the park. What about Xi'an? Hong Kong I'd allow at a minimum 2 days + 1 day for the park. Japan there is so much to do that you could do 2 weeks there alone + 3 days for the parks. Walking-wise it would be even for me as I like to leave the hotel room in the morning, come back before dinner to change and not come back again until bedtime. I remember in Disney Sea there was a day when we walked 25,000 steps (a lot of back and forth across the park for FPs). Shanghai Disney we had a VIP guide so we were able to make our way across the park in 1 direction, with a few quick double backs for 2 additional trips on Tron. The day we were in Hong Kong Disney it wasn't busy at all (it was humid and raining), so it was easy to cover the park in 1 day. Now if Disney would just open a park in Australia we would have a reason to go back
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I am from a big city, but the sheer size of Tokyo was shocking to me. You really need a few days just to see the sites of Tokyo using public transit (which is extremely efficient). I'm no help at all. I would need at least 2 weeks just in Japan. Hopefully some others can offer better advice.