Kevin I didn't take it at disrespectful. The model that I posted the panel lines are not gone. If you could see it in person you could tell. What I do is before I primer is cut the panel lines a little bit deeper so the clear coat won't fill in.
I strictly use urethanes paints (DuPont) To me they are the better then anything else on the market.
To answer some of your ?'s
#2 Hardener does have a shelf life, I can't tell you how long because where you live your humidity is different then where I live. The only way to make it last longer is to buy a can of Bloxygen. After you open your paint, hardener, & clear coat spray a little then close it.
#4 I mix my paint different then the next person its just a preference, I spray my paint at 15-23 psi.
#5 I use a paasche to an Iwata to sata airbrushes & a sata jet