Interesting subject, but by all means write the book. You will learn ten times as much trying to write it as you did before. What I mean is, to write a book means clarifying stuff so others understand. To do that you must be absolutely clear and thus you will focus and learn as you write. Just be forewarned, writing a book is tough work. No kidding there...
As for the jigs and fixtures. Well I do custom work so I never made them. At least I didn't. Now I am starting to go the other way. At work we build high end custom yachts, yachts that will only be made once and take years to build. They do a lot of jigs and templates for this boats despite that one of a kind thing. The majority of my work as a machinist is building the tools and tooling we need to make these boats. Our motto is simple. If we don't have it, we make it.
As a career, that puts me in the toolmaking category as a Tool and Die Maker. I never intended to get into this aspect of machining, but here I am. And I love it. The truth is, a lot of what I make is for the carpenters, so now I am seeing the benefits of jigs and fixtures for one time uses. That is slowly creeping into my woodworking projects too. Overall I think my woodworking has gone up a step because of this realization.
I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"