Welcome to disABILITIES.
I'm wondering what PC stands for (maybe "power chair??") since I've never heard that term used before to talk about a power wheelchair.
Anyway, I don't have much to add to what Lisa already said. More to reassure you that you DO want to back onto a lift. As Lisa mentioned, it is backing up onto a flat platform. That is the way that all wheelchairs, power or not go onto a lift. And you want to do it that way so the heaviest part of the wheelchair is closest to the bus.
Most of the buses at WDW are equipped with lifts, but about 2 years ago, they added some buses with ramps. Those are a problem for anyone with a power wheelchair, since any power wheelchairs should not be backed up a ramp.
If you don't already know, find out where the safe attachment places for vehicle tiedown are on your wheelchair, since they will strap/tie down your wheelchair on the buses. We use some bright pink plastic tape to mark the safe places on DD's wheelchair. It's a lot easier that way. I can just tell them they can attach to anything marked with pink tape.
The monorail station at the Contemporary is acessible, as are the monorail cars (or at least one on each train). The CM will direct you to the correct place to wait for the accessible car. Unless they added elevators in the last year, there will be a fairly steep ramp at MK and also at the TTC to get to/from the monorail station to the ground. The station is at the level of the monorail track.
You could probably call your airline and ask about your ramp. Ask to talk to someone who deals with special needs - they might say they don't have a "Special Needs" department, but they most likely do. That person can also help you with what needs to be done to transport the wheelchair. There was a thread a while back about someone's bad experience with airline travel. I'll see if I can find it and bump it up to the top.
If you want to check into renting a ramp, here are some medical equipment places to try:
Care Medical:
http://www.caremedicalequipment.com/
Walker Mobility:
1-888-726-6837
www.walkermobility.com
Colonial Medical
http://www.colonialmed.com/about_cms.html
If they don't rent them, they might know who does.
Get a GAC stating that your wheelchair is not an
ECV and you can remain in it in lines like Pooh.
ECVs are not allowed in some lines and some CMs may not understand that your wheelchair is not an ECV, because it doesn't look like a standard power wheelchair that they are more used to seeing.
CLICK HERE for the DIS Board's page about touring with a mobility disability. If you scroll to the bottom, you will find a list of rides/attractions where you can stay in the wheelchair for the whole attraction. For the ones where you need to transfer to a ride car, most of the time you will wait in the regular line. At some point before boarding, your party will be brought to the exit for boarding and the wheelchair will be waiting at the exit for you when you get off.
For the rides with a moving walkway, the CMs can slow, or even stop the moving walkway for boarding (except at Peter Pan - that one can't be stopped). At the Pirate Ride, you will have to switch to a foldable manual wheelchair because of the way that ride loads and exits. That one is the only big problem.