I've watched many great Sims 2 movies and series on Youtube and all of the Sims have been lip syncing, which is talking without any gestures at all; just moving the lips. Where can I get an overlay mod/hack that'll make my Sims lip sync??

Try decorgal21572. She has some amazing hacks and animation boxes.

First, pose your Sim using a posebox.
Then use this: Decorgal's talking hacks and your Sims will talk without moving their hands or their bodies.