Hi Brooke,
You can get a good view of the
Wishes Nighttime Spectacular from almost anywhere in Magic Kingdom, but to see Tinkerbell's flight well, it's better to be on the Main Street side of Cinderella Castle. If I were you, I'd probably try to find a spot near the walkway to Fantasyland (the one that ends at Mad Tea Party) or the walkway to Tomorrowland.
Wishes lasts about 12 minutes and is scheduled to start at 8 p.m. that night, so you should have at least 15 minutes to travel the short distance to Be Our Guest and arrive in advance of your reservation time. Just remember: you will be moving against the crowd, as many people head toward the exit when Wishes ends, so the walk may take a few minutes more than normal.
I'm sure you will all love
Be Our Guest. The interior is beautiful. I've been there for lunch and have our first dinner scheduled there a few days before your visit. We can't wait.
Make sure you save room for dessert. I especially like the Triple Chocolate Cupcake.
I hope that helps. Enjoy your visit!