i'm working with masks inside 3d objects made with teddy and painted with chameleon (from takeo igarashi software http://www-ui.is.s.u-tokyo.ac.jp/~takeo/index.html). just today i thought to make this, and i think it's very interesting way to give "more life" and get more fluid animations.
yes. you can. i didn't put nose just because my character never had.
maybe creating characters with noses will present a couple of troubles about how masking. (because the best thing is make the nose as an independent 3d object from the head)
but is just thinking and thinking and try to solve.