Here I'll add some informative info to redeem my past threads =P
Personally, I like the Classic look if it's a clean daily driver. Adds a more polished look. For this you would need some Adhesion promoter (SEM's, or Bulldog) and the paint of your choice. Be it spray bomb, or automotive urethane.
If it's a more rugged looking car or you want a little contrast, go black. Again, use the adhesion promoter since it's plastic, but I would just topcoat with some krylon fusion or regular black spray bomb. Super easy to touch up.
Don't worry about flex additive if you go the urethane route. This is only intended to keep the paint SUPER flexible for about the first 48-72 hours if you're installing plastic bumpers or trim.
Oh and last tip, regarding the header panel. FIND AN OEM ONE!!!!! Aftermarket ones are GARBAGE and fit like absolute crap. Especially the plastic ones.