No offense, but this is just going from the frying pan into the flames, fast.
You are going to put/instal stud or pad lettering on a substrate installed in such a fashion ?? Out of sincere curiosity, how is this sign being used ??
3D letters are usually reserved for very nice instalations like to a wall, a monument type sign or some sort of classy sign. Not an over-sized post and panel set up.
I know you said you are new to this industry, but how in the world did you land a job with expensive letters mounted to a piece of aluminum composite ?? Maybe I shouldn't've asked that question, but I just needed to know. Any pictures of the proposed sign in question ??