"I thing I would confine the technical stuff to the end of each chapter. Rather than trying to mix general content and technical stuff, put each part it on it's own footing. Don't worry about what you don't know or cannot find out for the first edition. Things will change. So make the book easy to revise by placing technical stuff together, but without making the book feel disjoint."
Another possibility could be an appendix or endnote style setup for the technical information. But that might be a bit disjointed.
Or go the opposite direction and stay technical with foot notes for examples of relevant gear.
Here's a more general idea regarding content: how did you get where you are now gear wise? This might make a good introductory chapter or something. It might not be for the first book but I could see this being used to explain your thought process behind the gear you took to Alaska.
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Keep in mind these comments are concerning what would have interested me when I started out on my lightweight backpacking journey.
"1- How geeky do I get? Is it reasonable to talk about R-values of sleeping pads, the water absorption rates of different fibers, and the nuances of LED technology?"
I think R value is a much needed discussion for many people in the "REI world" and water absorption may be as well.
Anything that relates to comfort and safety is probably worth delving into deeper. On the other hand for many people a light is just a light and they really don't care to much – you might stay basic in these areas. For example, without getting into different types of LED's you could discuss the benefits of regulated vs. non-regulated lights.
"2- How can I defend this book against inevitable attempts to dismiss it as a lightweight book?"
If it's written well enough it will defend itself.
"3- Given the changes in the publishing industry, am I correct in taking the self-publishing route, and printing a pre-edition that will be out for about 3 months before the full edition is ready?"
That's what I'd do but I'm the type that like to be self sufficient as much as possible. I suspect you are too. Such tendencies doesn't mean it's a good idea.
"4- What are the major weaknesses of other lightweight books? How can I avoid them."
Be authoritative and even confrontational but not dismissive.
When you dismiss things that have been working well for some people for decades you'll fail to win them over. However, if you approach it as the natural evolution and progression of what they're already doing then they're more apt to listen – you should open their minds to change before trying to change them. Show people why your ways are better instead of telling them they are. For example, consider the Christians who push their views on others in comparison to how the Bible says Christ operated. If you come across as pushy you'll do no more good than the self-righteous Christian does.
But, as always, there has to be balance. Like martial arts many techniques may have been pioneered long before you but you have to make them your own and teach them with complete understanding. Therefore, and if I understand what kind of book you're trying to write and the impact you're trying to have, I don't see this as the time to appeal to higher authorities. You have to become the authority in the eyes of the general public and present ideas with so much confidence it's as if you pioneered them. At the same time you have to keep from coming across as closed minded.
It's a big task.