Sorry I didn't reply sooner, been busy with Little League games.
Anyway, it depends on your waiter. We actually showed up early (I believe it was close to 7 PM) to request a window seat our last trip. And were actually seating quickly. So I talked to our waiter (Drew, he was great and a bit hit with my DS since that's his name) and he understood why I had a later PS (8 PM) and told us to eat slow and enjoy. He would not rush us at all.
I recommend around 8 PM, show up early and tell them you're willing to wait for a window seat.
I'm think you will be able to see Wishes if you are at a table away from the windows as long as you have a view of MK, of course. We, including people seating around us, let kids move closer to the window so they had a better view.
Hope that helps! Have fun planning!