I’d rather do +1D Steel because that’s the bonus you get for being nonhuman, which is an important aspect of witchers… but then I can’t find that rule. I think I made it up, maybe by extending the Faithful or Gifted bonus to Steel to all emotional attributes. Derp.
If you gain access to a trait as part of your LP, it costs one trait point, period. None cost two. None are free—even negative traits cost points.
I wouldn’t give witchers an extra belief. If they want to be witchers, they use the beliefs they have. If other things are more important? It happens, and it’s drama gold to have other witchers disparage you for getting caught up in politics or love or whatever instead of doing your job.
No one has ten spare trait points to spend on five spells. No one even has five spare. If you want witchers using the signs, give them a “Gifted” equivalent trait that either gives access or let them spend their RP on them as spells. But now you’re risking even more too-good lifepath-itis. Strong fighters and mages of a sort? Playing with fire.
You also have too many LPs. Now if you want to be a witcher you’re really going to spend your entire life being a witcher in witcher lifepaths than no one else can take. That’s slightly against the spirit of BW (although there are other funnel paths), it’s definitely less fun than having free and open LP options, and I’d say it’s not a good way to run a first-time BW game. I can see the problem; witchers in fiction are more like a combination of stock and lifepath. Like Elves, they really should be better than ordinary humans. But Elves at least give many options of what they do and how they live; witchers are one particular thing.
I still don’t like it, but I’d rather see the power concentrated in a small number of traits and LPs, which are “too good”, than have characters funneled into the equivalent of a stock, but with only one setting and very few LPs, most of them in a linear progression. Born -> Apprentice -> Witcher -> One actual choice. Boring! Give options!
Sadly, I think witchers are easy to make with a class-based system like D&D but hard to make mechanically with BW. Not that I don’t think you can have a game about them or play them. I just think you’re better off not trying to make mechanics for it.