Hi ilovemky!
You can valet at any Disney resort for no charge as long as you have your handicap sticker. Make sure you show it to the valet so that they know.
As far as the parks, if you are staying on site it is easiest to take the buses to the Magic Kindgom, because you are dropped off right near the front of the park instead at the parking lot on the other side of the lake.
The handicap spots at Animal Kingdom are easy to find, as you just follow the blue stripe on the pavement. MGM are very close to the front (just tell the parking attendant and they will point you in the right direction). The ones at Epcot are a bit further away. The last time I was there (they move them sometimes) they were on the right hand side of the front entrance. The parking attendants are very helpful.
If you have any other questions, come on over to the disABILITIES board, as the people there are wonderful and have all kinds of great ideas/knowledge!