Use the 87th Street or 84th St entrances, you should be able to access most of the park and the river from there with a wheelchair. I believe that the 87th St entrance also has bathrooms with ramps. Just avoid the 86th St entrance and you should be fine and also keep in mind there are a few hills so you might need some assistance.
I saw some wheelchair users but I'm not sure about accessibility
Yes, should be pretty good for you
Some areas, yes, most, no.
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