Yes you can take a Bus
I saw a lady trying to take the tour with her scooter. The driver explained that they couldn't accommodate the scooter on the bus. I'm sure if you needed to take a walker, I'm sure they can accommodate that on the bus for you
The bus tour requires you to stand in line, if you take the tour as soon as you arrive you are likely to catch a shorter line. Overall there is not a lot of walking as the visitor center and the Apollo center are not very large. A lot less walking when compared to say Disney, Universal studios, or Busch Gardens.
Main tour is by bus. Not abnormal amount of walking.
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