cai sxt air intake k&n

hi. I have a 2006 sxt 3.5 and I want to know: a) if DIY cais are any different from brand made one's like k and n. And I'm very sorry if this is asked a lot :P b) also I was wondering if this would even give the car any power or make it louder c) is an entire exhaust system worth it? or will...