Paper Animation Music Video

Really not much too it. It's the classic "the illusion of reality by being unrealistic". Pretty much everything in your example video is fake, most notably the extensive drop shadows that give the illusion of objects being layered, plus a few additional gradients and shadow effects here and there to create the illusion of occluded corners and such. For keyframing you can use posterization as already suggested, but oftentimes it will also simply boil down to create jumpy keyframes, meaning you go from pose to pose using hold keyframes rather than smoothly moving from place to place.

Mylenium

to simulate stop motion effects there are many ways, you can work with low FPS composition like 8 or 10 or you can use "Posterize Time" effects on an adjustment layer where you can lower the frame rate of your animation or simply you can animate each frame manually so you can get the stop motion effects you want, regarding paper texture, I think the best way ifs to prepare your scenes on photoshop then animate them in AE.