We were in MK last year on both Sat. and Sun. because that's how we'd made our plans/ADRs in advance, and it really was manageable. As has been said, you are routed through the shops on Main St. -- if you didn't already know it, the shops on the left-hand side (as you face castle) are all connected, so you can walk all the way through to Caseys and exit, turning left, over to Adventure land. I agree that Fantasyland was busy, but we happily made use of the "back" of the part (Tomorrowland, Frontierland, Adventureland) with no problems. We are going for the same week this year and have decided not to go to MK until later in the week -- just because we want to be able to walk right down Main St. to the castle when we first arrive, but please do not worry if you've already made your plans (and just think about if you do want to try to make a time when you can have your Main St. experience at a different point in your trip).