We saw Mickey and Pluto at many different times during the day up front between Main St. and the entrance. They would be to the right, just as you are walking onto Main street, in that circle plaza.
Also, you can see Mickey, Minnie, and Goofy in ToonTown at their meet 'n' greets. (all three have their own houses there where you can wait in line to take pics with them).
We never saw Goofy or Donald Duck while we were there. But we saw pretty much every single Princess! We saw Alice at the Casey Jr Train ride, she was helping people get on. We also saw Chip n Dale at the Minnie and Friends Character Breakfast at Plaza Inn (plus Baloo, Eeyore, Capt Hook, Tigger, Pooh)