I will give the rotobrush a try and look into the brush strokes. When I was working with the mask opacity I would set keyframes, and turn on the stop watch.. I had 4 keyframes. I set the first keyframe to 0% opacity, set the next to 100%, and then the third to 100%, and the fourth to 0% so that the mask was only visible in the short amount of time I needed it to completely obscure items beneath it. Any time I would change the mask opacity at that point, it would change it for all of them so I wasn’t sure what I was doing wrong. Considering I would end up having probably 300 masks before it’s all said and done the other two options may work better lol.