POR 15 questions

[tc4x4]

I'm about to start painting the under side of my bed, axle, springs, and other little parts. I'm wondering how I should go about doing this. I'm leaning towards por 15 for in durability but have a couple questions. I want it black but am not sure what por 15 product to use. I would think that the under side of the bed and other parts should be a satin black and the frame glossy or something. Is this a typical paint scheme people are using out there? When por15 says its semi gloss is that the same as a satin finish?

Should i use the por 15 rust preventative and then a top coat?