I just have read and re-read the FTC rules and searched all over the internet, but didn't find anything that would 100% clarify my doubts. So I really hope to get your input! My question is: would it comply with FTC rules to use term "18K gold g.e.p. (or 18K gold GEP, for that matter)" in item title? Or I can only use "18K gep", without word "gold"? It bothers me very much do not know it for certain...

You will want to be 100 % clear that this item is electroplated. By putting the word GOLD and then initials for electroplating it can be confusing. I would suggest GEP or gold electro plated. The clearer you are the less liability you will hold.