Follow the link in my signature or look near the top of this board for the disABILITIES FAQs thread.
Here are some posts you will want to check out:
Post 4: Riding WDW Buses with a wheelchair or
ECV - includes some picture links. As was pointed out, you can fold the chair and hold it on the bus or have it tied down.
Post 8: Parking, WDW Boats, Monorails, Specialty Cruises at the parks - this will be helpful if you take any boats or monorails. All monorails nod most boats are accessible.
Post 11: Basic accessibility lists for each park. Includes Mobility Access entrances from WDW Disabilities park maps, attractions requiring a transfer from wheelchair or ECV. If you want to bring the wheelchair into lines, ou can. You don't need anything o use it in line. If you choose to walk in line, you will park it by the strollers.
Post 15: Air travel, Orlando specific and some general travel hints - has information about gate checking your wheelchair. As was mentioned, there is no cost nd it doesn't count against your baggage allowance.
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Post 16: DME (Disney's Magical Express) - includes a picture of the stairs so you cn get an idea of whether the steps will be too steep for you.