3) Nah, has to be magic that's part of you and you're born with.
4) Eh, I sorta dunno about the Kishin-eggs, thing; in Soul Eater pretty much all bad guys are serial killers or blatantly evil, so this doesn't come up much...
Uh, I'm gonna say she's sort of? It's not like she was killing for the sake of killing or all that evil stuff. She's not really high on the evil-o-meter (which is pretty much what this is, measured mostly by murder) but I suppose her soul's a bit tarnished. This probably goes for a lot of the Leaf ninjas.