About the ammo. I wouldn't wish that neighbors are harmed from a stray round but, if someone comes into my house to harm my wife, I'll kill them. I don't really care. I preach practice for a reason. A round that is intended for a perp should kill that perp. If it passes through his/her body the likelihood of it going on to hurt an innocent is slim to none, but you have accomplished your goal. Practice to take out the perp with the first shot. Don't get shaky, aim for critical mass and squeeze, repeat as necessary. Blood and tissue can be cleaned up. In case you have to use a shotgun with .00 buck load remember things can be replaced, people can't, and the velocity of those projectiles reduce drastically after it passes through a human body (in fact, most of them stay in said body).
Practice for the real thing. Remember, don't "fire for effect", it only makes you a target. Fire the first, and any subsequent rounds, to kill, not wound, but to kill. Head shots are a rare thing unless you are highly trained for them. Aim for critical mass (the large part of the upper torso) and fire. This takes out great vessels, heart, and lungs, taking out the perp and causing immediate, or soon thereafter, death. Put this in your head and keep it there, you don't want to hurt this guy, you want to kill him. Or, he will kill you and your family.