I would say that 1" per 5 gal
is better but you are correct that individual situations are different. For ex. you PWC
schedule, feeding, refigium use, protein skimming....all play a role. The fish may not be crowded but to many nutrients can lead to algae blooms along with other issues.
However, I must admit I do not follow the " rule. Think about it, 2 3" Clowns would be 30 gal
? Keep in mind some fish are thicker and make more of a mess than others and that all plays in. I think your list looks fine but I know nothing about cardinals as far as compatibility.
I would stay with a Goby but that is because I love them. I think you will be fine with around 5 small fish and if everything goes well for months maybe 6 small. I think 6+ is to much. fish. I will probably get grief for saying 5. If you maintain good PWC
's. you should be ok.
I think you will do well since you display patience. Add them slow and adjust as you go.