Answer #1: Completely stable, yes.
Answer #2: I need to make each foreground layer disappear sequentially– first the small trees, then the forked tree, then the actor, then the background. The issue therein is that even when I perfectly isolate the planes, I still have gaps in each layer that I need to fill in as if the objects I’m removing were never there. If it were a still image, I would clone areas in PS– what do you suppose the best way to do this in AE would be?