Based on the day you are coming, it will be hard to find a spot on main street for the parade. South American tour groups are out in mass and are only supposed to grow this week. They will stake out main street as early as 6 or 7.
The outside right of the Hub will probably be your best bet if you want to watch all 3 from the same spot. Don't sit in the back left quadrant (where "the" is on the map" because you will not be able to see MSEP from there, though it is my favorite spot to watch Wishes from. It never fills up all the way and can be fairly unobstructed for Celebrate the Magic depending on where you stand.
The inside right ring of the hub is partially reserved for wheelchairs.
I wish I could offer more on timing, but I usually find my spot in the back left quadrant just before MSEP and watch Celebrate and Wishes, then catch MSEP for it's second showing, so I've never really checked to see how long people find their spots for the 9pm parade