Nice idea. I would suggest to identify a PARTICULAR "slice" of the night-sky (for example a costellation, and name the watch with its name, e.g. URSA MAJOR) to reproduce on the dial.
A problem could be the weight of the minutes hand: the "half moon" should me similar to the "half moon" used on the "pointer calendar" to keep the hand's balance during the rotation.
Seconds hand also needs its proper counterweight on the rear part (it should be a star, I suppose).
Enjoy the development of your project... ;)