1. Various audio effects can be utilized. Experiment with COMPRESSION, NORMALIZE, and AMPLIFY.

2, Use ZOOM or SCALE to enlarge the image slightly, to rid video of bottom-edge switching pulses, at the slight expense of image content.
3. Yes, certain choices can degrade quality. Choose a resolution equal to or less than that of the source material. Play with various quality options....

Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. Then you can restore a project to the state it was in when saved. Just double-click the VPJ file (which isn't playable).
If you make an error while editing, click <ctrl-Z> to backtrack, step-by-step. (Same as EDIT | UNDO)
Effects can be deleted by clicking the X at the right of a specific effect's menu bar.