I’m not trying to recreate Sapkowski witchers. I said that upfront. I’m trying to keep the essence of them, and I think that’s in fighting monsters. Being inhuman seems less important to me, especially in the books, than the perception of being something unsavory or evil, but a Char trait of Mutant with the reputation to go with it serves just fine.
What I am saying, poorly but repeatedly, is that I believe recreating the witchers of the books and games will give you a worse game of BW. You will have a better game if you adapt witchers to the game. Give up the silver and steel, the signs, the powers. Keep the monsters and the alienation. You can ditch the trappings; you just need the drama, and I think a first game of BW will be better off for being inspired by rather than explicitly set in Witcherland.
Let me back off a bit. You know your players. Do they all want to play witchers? Do any? Do some want to and some not?