In reference to your 4)
I had a guy working at my house doing some excavation in September. He had clothes he said he sent back once year to the manufacturer to get retreated with permethrin. I do not know the brand, but they were all a lite smooth khaki color. His shirt looked like one of those fishing shirts.
The only company I'm aware of that does this is: https://www.insectshield.com/Insect-Shield-Your-Clothes-P338.aspx