The two golden rules we learned after our first trip (and have found to be true ever since), are #1) Take your time, don't let anyone rush you and #2) don't be afraid to ask for what you need. You will find WDW among the most wheel-chair friendly places on Earth - the only sad part is that the rest of the world isn't nearly as accomodating.
That quote is so true and I agree completely with it. My brother has spina bifida and while he can walk, he uses a wheelchair when large amounts of walking are required.
The best advice that I can give goes along with AEfx's golden rules. We have found that the cms in the greeter positions at the entrance of the rides are great for answering any questions we have. The rides that have been built more recently typically have lines that are accessible and the older ones typically have alternate entrances such as the exit.
I hope that you all enjoy your trip!