With the gear you plan on taking, I don't know that I would use that particular backpack. I still think its a great multi-purpose backpack, but the last two times that I went to DL while trying to travel light (which for me is just one body and two lenses), I just put my gear into my regular daypack with the lenses in their own cases like
this. Made it much easier to carry extra stuff (jacket, water bottle, etc) and easier to get things in and out while on the move.
I still use the backpack you originally mentioned to store all my gear for day to day use and when I know I'll be needing to bring my whole kit.
One thing about that backpack though, I'm not that crazy with how it carries the tripod horizontal on the bottom. Mine keeps slipping off and makes it more difficult to set the pack down. My next bag will have vertical storage, but at Disney, you'll probably be better off storing it in a locker until night when you need it.