For example, I read that housing 3/5/7, etc finches together will cause aggression, and housing an even number (2/4/6, etc) will not. I have a Spice finch and Star finch and would like to introduce a Gouldian. The cage is 30x15 and I think 3 finches would be perfect. They would all be male, no females around to fight over.
Whitney do not get a gouldian finch they are meant to be housed only with other gouldians.
Weird thing your star finch tropical type and spice finch temperate are also not meant to be compatible as need to be with compatible finches in own tropical and temperate groups
So you have proved experts wrong but don't push your luck with the gouldian.
in answer as to even or odd numbers i think three could be the worst as two could pick on one and make life hell for the odd bird.
