I noticed you added the option to move layers around, this is nice! The only layer that I can't move is the background. Is there anyway you can incorporate a merge up for the background? I ask this because sometimes when I start to draw I do not know what the drawing will end up to be. Then if I already have sometime on the background layer and would like to add a background behind this? I love all of the functions that you have incorporated. Maybe I will go back in timeling and try to add background like that but never have been good with using timeline...maybe this is a good time to learn it. 
Maybe you can try this
You may try to add a new layer before you start. Just start drawing on the new layer, then if anything you are not sure, you can start another new layer. This is a good way to seek you target, every new idea start a new layer. But of course you have to delete your unwanted one to save your data space. Just leave the original background, sometime i find it's helpful to keep it there, so you can add or modify you drawing later, just treat it for enhancing layer.
Hope this can help you.
Cheers!
Drawing is about studying yourself and your target.