We've had dinner at Riverbelle and stayed in our seats for Fantasmic a couple of times just to have chairs. Getting there around 5:00 is a good idea but I've seen people get a table much later. It just depends.
The view isn't that great. And you can't stand up to see better. Thats a big No-No and the CM's will be right there to tell you to sit down.
The people in front of you are standing and also the CM;s are there with their flashlights directing traffic to keep moving. BUT you do have a chair so its a tossup.