Flying with a disability does have it's challenges, but the main thing to remember is prepare well and ensure that the airline knows about you and your requirements well in advance.
Most airlines have a special assistance team, who will ensure that all your requirements are met and tell you about preparing equipment such as electric wheelchairs.
Business class seats normally have more leg room and can provide more space for transfer. If possible fly using Premium Economy. This gives plenty of leg room and a more comfortable seat (if you are unable to stand during the flight this is a must).
Most airlines will allow you to take medical equipment free of charge in addition to normal luggage (please check) but they will need to know in advance.
Put medical equipment, such as battery chargers, slings, etc in a separate bag and label it "Fragile Medical Equipment". If you use a manual wheelchair you may be required to transfer into an airport wheelchair so that your wheelchair can be loaded into the hold.
With electric wheelchairs, you need to have dry/gel cell batteries installed. You will also need to have a battery isolate switch on the chair or be able to easily disconnect the battery for the flight. You will take your wheelchair to the door of the aircraft. At the door the ground crew or your carers will transfer you to the aircraft aisle wheelchair and take you to your seat. Before leaving your wheelchair put the wheels to manual or give the ground crew instructions on moving the chair.
Parking at the airport,Gatwick Airport has good transfers from the Long Stay car park but it is worth booking long term parking in advance.
Please check with your airline and airport.
Flying from London Gatwick to Orlando (MCO) is a 9 hour flight, but you will probably be first on the plane and last to leave. Take a bottle of water with you for the flight (purchase air side) then drink plenty, this helps reduce jet lag. Now that you have drunk a lot, toileting becomes the problem. If you can stand and get to the aircraft toilet great, alternatively it is worth talking to a continence advisor or your doctor for ways of coping (even if it is not normally a problem). A blanket and bottle may work, or look at the products supplied by Sauer ContinenceandBeambridge.
If you would like any further information I would be pleased to help.