I have a 20 gallon tank with 6 guppies , 5 albino cory cats [ they stay really small ] , 5 ghost shrimps , and 3 fish that are transparent and stay small [ cant remember name ]. With live plants ?
it sounds ok. i would not get any more fish though. the whole thing with overcrowding is bioload. bioload is how much waste the fish make and how much your filter can handle. luckily the ghost shrimp have very small bioloads. the smaller the fish/invert the smaller the bioload