You should make an ADR for 2 hours before Wishes is scheduled to start that night. We had 7:30 ADRs on a night when the show started at 10. Our server did his best to pace the meal so that we would be done right when the fireworks started, but dessert was delayed so we had to leave our seats in the middle of our creme brulee to watch Wishes. Not a big deal for dessert, but it would have been bad to get up in the middle of the entree.
We didn't have window seats and so had to get up to watch the show on the outside viewing platform. Of course, outside is how fireworks are meant to be viewed so I can't imagine that the experience is inferior to watching from your table. So go ahead and request the castle view, but don't sweat it if you end up with some other view. Also, watch Wishes from Cali Grill BEFORE you watch it in MK. Since the show is designed to be viewed with the fireworks framing the castle, seeing Wishes from CR could be a letdown if you'd already seen it from Main Street.
Request Ron as your server; he was a gem. Enjoy!
Lee