I'd have to 2nd the recommendation for the Mickey Ave at MGM. It's Sorcerer Mickey too - which is kind of neat! It's also inside - so even if there is a line, you get to stand in the air conditioning! (And the line moves much faster than the one in Toon Town) The daily guide map will also tell you which times that Mickey is there so you can plan a little better.
If you are looking for a dining experience with Mickey - I suggest the Garden Grill at Epcot. They have Mickey, Pluto, Chip & Dale and the entire restaurant revolves while you are eating. It's family style food - which means it's a buffet where they bring you whatever you want! Much better than having to get up and get it & you know when they bring you the food it's hot & fresh. I think it is one of the better value meals at WDW also, b/c we are always stuffed when we leave & it's not an incredible amount more than counter service! (And if you go at lunch time, I think it may be even less!)
Good luck - it's always great to see the Mouse!