Most coaster brakes are easily dissembled, cleaned, repacked, and re-assembled. (Some take oil rather than grease on the shoes, and grease in the bearings, but most of them take a buncha grease throughout.) Adjusting the bearings is really easy, once you get the hang of it. Some folks have a tendency to adjust'm too tight, especially the guys at the KT factory-- all kidding aside, most new KT and Shimano hubs come a bit tight from the factory. You want to find the sweet spot between "loose" and binding. If you can't get it 100% right, better to go a tiny bit loose than a tiny bit tight. Deorman linked to the how-to manual; there are plenty of repack how-to's on RRB and elsewhere on the internet. RRB member Udallcustombikes has a series of threads call the "UCB hub project", where he sacrifices hubs for a tear-down, and then cuts away part of the shell so you can see the innards after it's re-assembled. In my opinion, those threads are among the best on the site.
As for soap, you get that when you mix a fatty acid with an alkali salt. You can boil pig fat (lard) to render pure fat, with almost no impurities, but afterwards, you'll need to mix lye (or potash, if you don't have lye) with water and then mix that with the fats to make soap. It's more complicated then that, b/c you need precise weights and measurements to get the ratios right, and then temperature plays a big part---it's a big hassle, unless you happen to enjoy it. (I make and I sell soap--- which reminds me; I need to make more for a fund-raiser ASAP...so that's how I know about soap-making.) Not to be pedantic, but I believe that the additives in grease are detergents, and not technically "soap" in the traditional sense of the term, but i might be wrong about that. I haven't started making any DIY grease yet....