Using high temp paint on a header will help reduce the amount of heat that gets into the engine bay, right?

Also, will high temp paint prolong or reduce the life of a header?

 

High temp paint only helps the paint not to fade as quickly as regular paint because it's heat resistant. I don't think the paint will prolong the life of the header.
I just purchase some USED Dc Sport header form this sight and are just a little rusted and I'm not using heat paint instead I will Powder Coat them . Powder coating lasts way longer than heat paint

 

I got anuncoated Pacesetter header. I'm wondering if I should coat it cause I've heard they can crack from heat.

 

Any kind of coating or insulation will make the pipe run hotter. More air circulation is the only way to make your pipe cooler.

If you're running too lean your pipe will definately overheat.