A lot meaning that for many of the tourist destinations, you'd be walking at least a block or so (and that's if you get dropped off at the door of the attraction - there's a whole level of walking just to get there). Forget public transportation - most would require extensive walking and probably stairs (some of the biggest train stations will have elevators but most do not). Japan is horrendously equipped for disabled people. A tour may be different if it's a bus but not sure. I'd talk to a travel agency that's experienced with Japan and disabilities and see what they recommend.

Masaki