Have your subject pick up real pieces of cardboard with large black dots in the four corners. Then use a 4 point motion track to animate your glowing cards. Put a duplicate copy of your footage above the cards and rotoscope the fingers and hands.
Follow THIS tutorial too ease some of the pains of rotoscoping.
There are several ways. Head up to the menu and select ‘Layer’ – ‘Time’ and choose which route you’d like to take. In your case I’d probably time remap for the greatest control over when the layer stops proceeding and starts reversing and the speed at which it does it.
I’m not questioning your intelligence and I know this kinda like asking “is it plugged in?” but I’ve gotta ask. Is your paint stroke the same color as the background of the comp?
Fractal Noise with an animated threshold should make a good matte for the reveal.
Maybe use two. The first would have a low contrast for the broad spreading. The second would be more complex with a higher contrast to create splotches.
You can make a matte of your keyed footage for use after it’s tooned. Also, it looks really cool if you follow the tutorial about adding a stroke around your actor.