I think if you get there at opening, head straight for Fantasyland, you'll be able to get all the rides done by 10:30am. And yes, get to Dumbo first!
Toontown opens at 10am, so head there when you are finished with Fantasyland. Then take the "secret" path from Toontown to Tommorrowland. You can get a ride in or two before lunch.
If you don't get to MK at opening, then you may get hit with the crowds. I know they say Mondays are bad at MK, but I know reading the posts on here everyone is saying Monday mornings at opening aren't too bad during the slow season.
HTH