sam2, I know that you are very enthusiastic about your learning but I suggest you check your sources first. Rambam,hilchos “rotzeach ushmiras nefesh” perek 2, mishne 7 and 8(free translation): “one who murders a healthy man or one who murders a sick man that is near death (goises),and even if he murdered a “goises” himself, he is under the penalty of death. And if he is a “goises” by the action of a human being, being that one beat him till near death (and the second one murdered him), he (the second one) is not liable for the death penalty”
Mishne 8: ” the one who murders a ‘treifa”, even thought he (the treifa) goes about town and eats and drinks he is not liable for the death penalty “bidei odom”- by a human bais din”,and every person is assured (bechezkas) that he is a healthy man unless you know for sure that he is a treifa (and therefore anyone who murders a person is liable to the death penalty)
so- yes, if you kill a ‘goises” you are “chaiyv missah’ and if you kill a ‘treifa’ you are not “chayiv missah”. simple fact.
I’ll answer your other points in the next post.