Why a guy essence? is woman essence prohibited?

nope don't think so. just seems like he likes guys more. maybe because the female wolves treated him badly when he was still in the cave...
but an interesting question you got there :)

Both are fine. I think gal hardly walks alone so it's more difficult.
Other werewolves live as couple and taking essence from each other.
Too bad the gal that the village head arranged for the Uke, refused him.
http://www.mangago.me/read-manga/hakuyou_ayakashi_gatari/sa/sa-c001/10/

Thank you for the answer ~~