I dont know how well this would work...I dont especially like it, but then again, I have never been killed, nor have I hired an assasin. My ideas were to make the killer descend deeper into darkness, giving a little bit more substance to the role, with things such as killer not being able to speak in chat with the exception of some scenes, the possibility of many people to ”grab” an assasin, just like you do with a fugitive, and send to jail/other nasty stuff, eliminate the grey traces, eliminate the avatar or change it randomly every week etc etc
I admit that the idea of a warrant officer makes (a lot) of sense, but I dont really like it.
P.S. I am really curious to see who would answer your nr 3 question.