All i can say is do your homework!
i have a guy that is BPI certified, He can help you with all the pros and cons in person. I have been with him on a few quotes, he knows what hes taking about. Not biased to one insulation over another.
At the least call a few insulators in the area and gain some other opinions that see it in person.
Welp.... Yes, I agree to a large extent. Seek advice from those that live an work in your locale.
However- I am skeptical of blanket rules and codes purportenances. Common sense and practical solutions to common problems trumps ALL. In your case- no permit and no inspection would mean you are merely an idiot, and not smart enough to know better- which is negligence. Stupid is defensible, Negligence is actionable.
But yes Too. Your graphic is good. Excellent.
Yes absolutely, getting the radiant barrier correct is the sole key. I dislike plastics. You use insulation both ways.
You don't need much of a nailer, A 3/4" x 3/4" (or 1x1" )strip can be nailed with a trim gun, and the thermoply can be nailed up with a slap stapler or staple gun. From what I saw of your pics, you should have an easy time putting up a tight bit of insulation- properly.
When you have the thermoply, set your blade on your razor knife to extend out about a smidge to cut a wall flap, not enough to cut all the way through the foil side, and score a line, it will fold nicely on that line and not seperate... This after you cut some rips out of a full sheet. You got 16" centers, you get three 14.5" pieces x 96"... or two at 22.5". Score a transverse "flap" at 10" (you have a steep roof IIRC 12/12 P so 10" may be enough to "returnt o the the Wall vertically above the ceiling.) Install the "Wall up the rake" piece first. Then flap another piece as needed (height of nailer) and install top down. Cut filler pieces flat.
I may need to look at your pics again, but only to see the run and rise.....
Thermoply, a trim nailer, and a roofing coil nailer are the hot set-up. A trim nailer is about the only way to get the nailer in place, and it only has to be be big enough to be nailed, the air gap you are providing at 1/2" is PLENTY....
Feel free to PM me for me Phone Number, and I'd be happy to talk with you tomorrow while at work....
GeeVee