Hobie,
In answer to your first question, take a look at the journal article posted at
https://www.mja.com.au/journal/2000/173/11/shotgun-suicide-difference .
With any defensive firearm, there are two basic factors at work in stopping an assailant: projectile placement, and projectile penetration. Both are critical, neither usually works too well alone/in isolation. Placement is mostly up to the shooter, penetration is mostly up to the firearm and ammunition used.
Keep in mind - for any number of reasons, a defender might only get ONE shot in a given defensive situation. I don't count on getting followup shots, and I wouldn't start off with an ineffective load with the idea in mind that I'd be able to shoot again if I needed to.
I've heard the "#1 buck is best" schtick ever since my first hunter safety class forty years ago. I have yet to find a shotgun that patterns #1 buck worth a darn. I'm told they exist, but I have yet to find one. On the other hand, I have little trouble getting pretty much any size pattern of 00 buck I want these days, simply by changing manufacturers/loads. I experiment with a good many loads and shot sizes, but what I keep loaded in the 'house guns' is Federal LE-127 00 with Brenneke KO slugs in the Sidesaddles.
Give Clint Smith a look at
http://www.youtube.com/watch?v=JhJ-p-72p8Y and consider buying the video from which these clips are taken, or equivalent productions from Louis Awerbuck, Tom Givens etc. If you can manage it, take a defensive shotgun class from a good instructor. IMHO your ability to run the gun under pressure and hit what you shoot at is ultimately more important that what comes out of the muzzle when you press the trigger.