I've never heard this word used in normal speech so it must be a very obscure word. According to the definition, it has to do more with the facial features, facial expression and their qualities. I hope this helps some.

"Countenance" is almost never used nowadays, although Shakespeare used this word quite often. "Countenance" can also refer to the expression on a person's face as well as the physical appearance. Yes, you would probably use it in a literary context.