I pretty sure there is a shuttle b/w parks (SW, A, DC), but we didn't use it so I'm not positive. We saw a SW bus when we did the shuttle from our hotel.
Not sure about credit cards, but I can't imagine they don't take them.
You can show your receipt from one park for the other. They will keep it and give you a new one. Just be sure your SO doesn't throw it away when he takes the car for gas AFTER you tucked it safely into the compartment in the console. I made him go back and fish it out of the trash bin