I ended up approaching this from a pretty literally. As I started thinking about what a mystic, old west, gunslinger would be I realized that it'd be interesting and plausible to cast him as a wiccan, since witch hunts continued right up through the end of the 19th century. This lead me to think about how his witchcraft would shape his life, and in the 19th century, practicing wicca would surely make you an outcast from American society, leading him to affiliate with the American Indians. After some research into wiccan and native american theology, it became clear that there are some strong ties that made the pairing perfect. Animism, a concept of Mother/Father god dualities, and a holistic, natural approach to life are present in both.
That's how I landed where I am with this guy currently.
I based his features on Charles Bronson because I love how in his cowboy films his ethnic/cultural background is flexible. I feel like that adds to this character's outsider-straddling-two-worlds mystique.
Upon stepping away from this for I bit, I've noticed spacing/anatomy issues with his eyes and face. I'll hit those on my next pass!