Gotta go with some of the opinions expressed already. You're already over the max, IMO. I think Bang may've been joking about the neon. My take on it (forgive me and feel free to correct me if I'm wrong, Bang, as I wouldn't want to put words in anyone's mouth) is Bang was saying that with being overstocked as your fish grow and a tang's propensity to develop ich you would need another neon goby just to keep up with the ich outbreaks!
And about the sailfin too. It may SURVIVE in a 30 gallon but it's certainly never going to THRIVE! It's cruel, IMO. When it reaches it's max size (if it ever does and doesn't die first) the poor thing will barely be able to turn around much less really actively fly from one end of the tank to the other as tangs like to do. A fish can get used to some REALLY awful conditions as long as they happen gradually and slowly but it doesn't make it right. Not to mention that there's an exception to every rule. There are a few posts on here in the past where people don't do water changes, have readings off the charts, and their fish continue to live. Would any of us say that because of those few exceptions it's ok to never do water changes as long as the fish live through it? Not me. Children survive with being brutally beaten every day for years. Damsels survive the cycling process very often the whole while tortured while the ammonia burns their gills. Cockatoos survive not having their mental and emotional needs met to the point that they desperately mutilate themselves. It's still cruel.
I'm not the least bit scared to put fish in a tank and my opinion is not even as conservative as some. I think one inch per 5 gallons is the safest bet although I prefer to use that measurement for keeping fish in a reef tank and for fish only will go a tad bit more fish. No opinion on these "inches per whatever rules" replaces very carefully researching the max size and such of every single animal you consider before buying and having the patience to stock a little at a time though. These "rules" are just crude starting points, people's opinions, and not to be taken to their literal extreme.
