Overall, I did a search and came up with :
http://www.mssociety.org.uk/forum/everyday-living/mobility-scooters-travel-air-or-sea which definitely has decent advice. Most of it seems to come from a former BA employee who now is disabled.
1) You will probably need an adapter that also is a power converter. They're bigger, chunkier, and more expensive, but still probably not as expensive as a US charger would be. If you decide to look into buying a US one, you'd need to contact either a local place that sells wheelchairs/scooters and ask them to order one or contact Pride to see if they know how you can get one. (
http://www.pridemobility.com/contact.asp) Pride would also know if you need something to convert the charge or not. I know you must for some powerchairs, but scooters may charge differently. Generally if the charger says on it something like "input: AC100-240V", you should be fine with an adapter that only adapts the actual plug (doesn't convert voltage).
2) I can't help you here. Depending on how the plugs are located, they may not work as well with any adapter that also is converting voltage just because those are usually pretty big.
3) Isolating the battery just means making sure that while it's traveling, there's no way for the
scooter to turn on. Depending on the type of your battery (another question for Pride, if you contact them), you can probably just take the key out and be fine. If that isn't enough, you'd need to disconnect the battery from the controls. Either way it can stay in the scooter. After you do this, you should still it in neutral because you don't want someone to try to move it while the wheels/motor are locked. All of the isolating can be done at the door of the aircraft (called gate checking).
I highly suggest bringing written instructions abot disconnecting the battery, putting the scooter in & out of neutral, so that you have the reminder for yourself and to show to the airport ground staff. The best would be to have something laminated and attached to the scooter (just for flying) with instructions both in English and Spanish. If you can't manage the Spanish, don't worry about it, it just would be more convenient for the Orlando ground staff (in many places in the US, Spanish is the native language of many/most of the ground staff that actually load/unload). You also want on that sheet to put very large and clearly that the scooter must be loaded & placed upright in the hold. Even if you don't want to give instructions for everything to do with the battery, putting a sign on it about the upright is the absolute most important information for them. (The second is probably how to take it in and out of neutral.)