Disney World Resort hotels all have different levels of HA (Handicapped Accessible) rooms. You can find everything from tubs with grab bars, to "Florida rooms" to Roll-in Shower rooms. If you want to stay on property, you may have to call Disney, and have a Cast Member search for the type of room you want; some Resorts may sell out earlier on those room types than others.
We only stay on-property, so I can't really comment on offsite hotel rooms; I require a roll-in shower these days, and those are more difficult to find (for example, Swan & Dolphin apparently have none, and I think there is only one of the "official" Disney Springs hotels that has one).
Be sure to identify what you need as far as the *type* of HA room, and start your search from there.
Airlines should all be about the same. Do allow for some extra time, and get to the airport early to allow extra time for TSA, as well as boarding. Most airlines these days will board the passenger + 1 "helper" early; the rest of your party may have to wait with everyone else. Let the airline know if you need an aisle chair - the special skinny chair that fits down the aisle of the aircraft. The wheelchair can be gate checked, but make sure that you don't leave anything personal attached to it, or anything that could fall off, or get caught on something else in the aircraft's hold. Things *do* shift during the flight, and you want to minimize the opportunity for damage.
Typically, when flying, it's just like the buses at WDW - you get on first, and get off last, so plan for slightly longer layovers if needed. It can take up to 20 minutes for some airlines to get your wheelchair upstairs from the hold, so you are almost always the very last people up the Jetway.
As far as rental vans go, I have zero experience there; we let Disney do the driving. Too many tourists and construction for this old Rabbit to be driving around down there!
