Okay guys Im not a newb to cars but I am to this newfangled plastic stuff.
Ive got a bit of a background with fiberglass but the urethanes and stuff are new to me.
Anyway here goes.

1 How do I fill the 2 holes some **** put in the front bumper where they mounted some junkyard refugee plate holder.

2 the OEM rear wrap around wing is apparently a steel frame covered with "some type of hard rubber." It has many cracks in it from shrinking. can I open the cracks up with a bevel on each side and fill with some sort of epoxy ike a marine grade? Then skim with a plastic filler? Ive repaired cracked steering wheels ( 2 1955 chevy wheels) using a similar method. Im concerned about the filler being too "hot" and destroying it.
My other options are to find a NOS or junkyard one; which might shrink under my new paint and REALLY piss me off; or, buy a replacement FG one for about 400 bones...simply not an option.

Also, are there certain primers I should avoid aside from an Etch, which I wont need to use because Im going to DA the whole car anyway.

Thanks for the help folks

Usually it's best to get with your local paint jobber to identify the type of plastic and then figure out which fillers adhere and flex the best for that application. A few materials you'll see around for this are 3M Automix, Duramix, USC's Thin Ice, etc. I think that rubber crap on the wing is what was loosely referred to as Enduro (not sure about that) which is the same rubbery crap that Pontiac Fiero's had in their front bumper cover. Can you fix it if it's cracked up that bad? I dunno, epoxy does heat up as it cures. How hot it gets depends on the mass of the fill. For example a two ounce cup fully mixed can get up to 180 degrees as it cures. Think I'd try something like one of the bonding glues made by Fusor down in the crack and use something like a flex bondo (USC's Thin Ice is good for this) to top fill. I think the biggest test for all of this stuff holding together will be setting in the hot summer sun and the later cool off. Personally, if I liked the style of the thing, I'd just fill it and take a mold off of it, and build my own replica out of fiberglass.
I prefer epoxy as a primer on most everything.

There is usually an ISO Code on the back of plastic so you can identify it. Its usually an acronym example (PP) for Poly propelene. When in doubt take it your local jobber like mentioned. Good luck