If you must use adjusters, I have found a few, abiet a very few, instances where a good adjuster would be better than a removable double overhand knot, These could easily be made. Hey, Mr. Lawton, you listening?? A drill press and a simple jig are all that is really needed for this, sandpaper, or perhaps some sort of flame polishing to remove any sharp edges. Maybe a needle file?
Fine fishing line is OK for guy lines. I agree with David about the multiple use of that stuff. That said, I do not use it for bear line. It cuts into bark or wood and can hang up trying to retrieve a bear bag. 1.5mm is better for 10-12pounds of food.
Braided fishing line works well. Fly line backing even comes in Spectra and coated. 40pound is a real 40pound test, not 26pound. It is, however, quite slick. Many knots do not care to lock into it well, soo, I use fishermens knots, double overhand knots for loops, melted ends, and loop-to-loop connections. A bit of a pain to set up, but relativly permanent.