Having done Disney in a boot I can agree it's going to be hot and sticky. It will smell awful if not properly cared for. The sudden Florida rain was also a complication I didn't plan on. We ended up in a gift store and were given one of the large, now extinct, plastic bags by a wonderful CM to cover my foot so we could make it to a fast pass. That said, bring something to wrap their foot in case of a downpour you can't avoid. A large, thick, plastic bag tied above the boot will have a similar affect on the foot to one of those at home zipper saunas but will also keep out rain long enough to get from point A to point B if necessary. The bottom of the bag does wear out after a while.
After park care for the boot, tear it down and let it air out as much as possible.
For the person, ice packs will likely be a lifesaver. They were for me. Every night and every morning before heading out I was working on keeping swelling down.
We did take frequent breaks and at meals I kept my foot elevated. We also visited a lot of attractions which involve sitting for an extended period of time. We also did not crisscross the parks if at all possible to minimize walking. They may also want to look into getting the disability pass (forgot the official name) for this trip depending on how bad the injury is.
