Re: the animation. I think it can be very effective to emphasize a point, or just add a playful thing in there. Not necessarily mouth open/closed, but for example in a conversation where the eyes look at different things, hands that clasp, or a change of hand positioning, or even a small background change (like a person or a car travels across). But I would limit it to small things - they're nice, they're cute, but they are not the most important thing.