I remember reading material that you've mentioned. All this is so interesting to me and I could spend (have spent) hours and hours reading just for the sake of soaking up all that I can--for knowledge sake. It's time-consuming and labor-intensive so, yes, one needs to understand all the ins and outs before delving into making pioneer-style soap. You bring up really good points......as usual. I hope I live long enough to become as knowledgable as you .Remember too that ashes vary in composition, so the resulting soap will vary too.
If you make soap using ashes from inland woods, your soap will be softer than soap made with ashes of marine or seacoast vegetation.
Many ancient soap making centers were usually along ocean coastlines, because soap makers could harvest and burn seaweed and other specific plants that were adapted to living in a salty environment. These ashes contained more sodium than ashes from inland woods, so you'd get a firmer soap.
Also, you want to use ash that's been burned to white, not softwood ashes and not black ashes. Softwood ash contains less carbonate so the ley will not be as strong, so hardwood ashes are preferred. Black ash contains more impurities.