Yes
Yes
We are all deserving of death, but, apparently, God believes that we are all also deserving of salvation.
If I were sinless I wouldn't need salvation. The very fact that salvation is available to each and every one of us means that sin can be forgiven.
Yes
That is not the same thing as Paul saying "stone this person for {offense}". This is Paul saying that if he has done anything deserving of death under then he is okay with dying. You still need to show where Jesus or one of the Apostles said, "Stone them".
As to the thief, is it not true that we are ALL deserving of death?
We are all deserving of death, but, apparently, God believes that we are all also deserving of salvation.
If I were sinless I wouldn't need salvation. The very fact that salvation is available to each and every one of us means that sin can be forgiven.