Part 1: Boundaries:
The boundaries of a stage involve two parts: the Camera and the Death Boundaries. Select the CamLimit0N, CamLimit1N, Dead0N, and Dead1N in the bottom left corner. Play around with the X and Y coordinates of the CamLimit0N, CamLimit1N, Dead0N, and Dead1N. Try to keep the death boundaries out side of the camera.
When you finish and have boundaries that match your stage, don't save!!! Open Notepad and record the coordinates of each point. Then, without saving in Brawlwall, open the stage Brawlbox. Go to MiscData[100] and view the model. You'll see a bunch of green lines, bones. If you look at the bone names you'll find the boundary points! Here you can edit each point in Brawlbox. When you finish, you can finally save.