Couple questions on prepping some body parts!

[MoNsTaMaCk24]

I got a 99 Civic SI I use as a daily driver. Im getting a little bit of rust spots above the windshield. So figured to heck with it... Im bringing this thing up to par. I use to do a little bit of body work. I figured I could spot prime spots and fix dents and just have a local body shop or maaco spray the whole thing. I need to prep a mugen front lip and an oem looking rear lip made out of abs plastic. How should I got about them and what primer should I use on them? After i grind down rust spots should I use a self etching primer? Or simply body putty fine? Is the spary can primer I can buy at auto zone fine for flexing? Any help highly appreciated!