I do my own paint on my car with spray can, and have had very good results. In my opinion 40th anniversary quarts is the most difficult paint to match with our Z's. Here are links to my threads.
DIY Paint Project #2 Rear Spats progress... with question?
DIY- Painting front lip progress!
Advice for you, I can tell you that you will need adhesive promoter before you lay down your primer. Primer directly sprayed on urethane will not stick. In my opinion frp or fiberglass is much easier to paint for a DIY, but it doesn't mean that it can't be done with urethane. Also remember to use 2k clear (2 part paint)!
I get my products from automotivetouchup.com, their paint match has been great for my projects, good luck!