There is an outdoor patio on the far end of the 4th floor (opposite end of same floor as Chef Mickey's) where we enjoyed watching the fireworks the last time we stayed there. Avoids the crowds exiting and several places to sit. Electric Water Pageant is on the lake is also fun to watch. Our room was on the lake side so we could watch the Electric Parade from our outdoor patio. I would imagine you can just walk outside by the pool areas to watch as well. As someone else mentioned, the time shifts around based on when the MK fireworks show/park hours.
Some nice gift shops also on the 4th floor. Not really much else to do there. The floor numbering relates to the difference in elevation on the property. The check-in desk is on the lowest level when you enter from the street, I assume that is considered the '1st floor'.
Depending on how early you are eating, you can also hop the monorail and visit Polynesian or Floridian prior to the fireworks.