You will probably have seen African Cichlid tanks with those kind of numbers, American Cichlids are totally different. Cichlids here is an umbrella term for a type of animal really.
Its just so different, someone explained it really well the other day and I'm sorry I've forgotten who! Its just really good and I dont want to take credit.
A lot of the Rift Lake African Cichlids carry their young in their mouth so the spawning site and territories move constantly and they get enough space because of it, they also live in a very cramped conditions in the wild so the overstocking techniques work because it spreads out the aggression. American or New World Cichlids make nests and actively defend a territory when spawning both through the egg stage and when raising the young. Even if you dont have pairs that instinct is still there and they all want to claim something for themselves.
@itiwhetu 's tanks are amazing but I've never known anyone else have that level of success doing the same thing. Most others end up with dead fish so its not something I can recommend because it feels like an exception rather than the rule. My advice comes from a place where I think its likely you are going to succeed longer term with the ambition of the fish living to their natural life span of 10-15 years. But this is not to take anything away from Itiwhetus fish or tanks because like I say they look incredible
Its pretty likely as your fish grow you are going to get a good idea of the fact you will need to reduce the numbers because your fish will get stressed or you will see fights or you'll see damage on the fins and bodies etc. There is an outside chance that it does work but you would probably be over stocked with 12 chunky 4-5 inch cichlids in a 30 gallon tank. Even on the low side you'd have 48 inches of chunky fish in a 30 gallon tank so likely to have some issues and elaborate maintenance routines.
Wills