On question 4, the dark knight soul crystal doesn't do anything like that, though it seems to have a certain level of... autonomy? At least, it produces a Darkside of the WoL on contact.
On question 5... We don't know? the lorebook states that if the Abyss isn't controlled, it will immolate the wielder in black fire, not unlike what can happen to weak Black Mages. But we haven't been given an example of someone who does not have good intentions; that is, someone who is sociopathic and already as callous and self-serving as the WoL's Esteem and then some. Will they just auto-immolate? We don't know. I have the feeling that the Dark Arts in the hands of someone like that would get very Sith-ish very quickly though.
On question 5... We don't know? the lorebook states that if the Abyss isn't controlled, it will immolate the wielder in black fire, not unlike what can happen to weak Black Mages. But we haven't been given an example of someone who does not have good intentions; that is, someone who is sociopathic and already as callous and self-serving as the WoL's Esteem and then some. Will they just auto-immolate? We don't know. I have the feeling that the Dark Arts in the hands of someone like that would get very Sith-ish very quickly though.