Headers
#1
#2
Its not cheap, $500 un-shipped usually, OBX makes good stainless headers, Dynatech makes the best for $880, or $1400 with hi-flow cats and extensions. I would hold off on headers because you stated your main goal was to keep sound down a bit. If you one day wake up with the craving for more then go for it. I especially wouldn't put headers on it until your done paying for it.
#4
yeah, LTs, hi-flow cats, and an 18" Magnaflow is loud, so yeah . You best hold off, plus its such a PITA install on these trucks, the easiest thing is literally pulling the front clip off and working because of the vast array of angles and the stud bolt issues, not worth the fight unless you're planning to get every bit of horsepower out you can.