I don't tend to get to caught up in the whole "designed for the military or le thing," those slugs may be great, but so are their K.O. slugs, which you can get in a box of 5 for a few bucks, similar with the Remington Green Box 00 I use. A for defensive purposes, a slug is a slug, it's a big chunk of lead to penetrate cover, for hunting with rifled barrels its a bit different.
As far as distance for patterning, really, that is something you need to determine, but my thinking is, figure out the longest shot you plan to take inside your home, and shoot that distance, (say 10m), then divide it in half, and shoot that distance (5m), and then if I had the rounds, time, and space, I would double the distance of the longer one, and shoot that. Because gunfights and SD situations are dynamic and changing, and it is always good to know the capabilities of your weapon. Different rounds are going to pattern differently too, so that is something to watch out for. But that is all just my opinion.
Also, when you get the shotgun, work on learning how to use the recoil of a shot to help you work the slide, that makes for faster follow-up shots.