Why the limitations to one God?
if there were two gods, they would have to differ from each other in some way. But a being that is pure act (without any potentiality) and absolutely simple (not composed of parts) cannot have any accidental differences. They could only differ in their very “whatness” (essence). However, if they differ in essence, then one has a perfection the other lacks. The one lacking that perfection would not be absolutely perfect, and therefore would not be God. Thus, you cannot have two beings each claiming to be the maximum of being.
I mean, God, isn't one enough? Honestly, it's too much for me!
More realistic than god.
No argument there, but “in nature everything has an opposite” is just as illogical; many things have no opposite, thus it’s not “at least two” it’s zero asshole gods in a nihilistic atheistic universe, one asshole god in a true monotheistic universe, one neutered god and one not-quite god representing the bit that’s been neutered off in a false monotheistic universe, one good god and one bad god in a morally balanced duotheistic universe (looks identical to the zero god(s) option), or a variable number of variably asshole gods in a polytheistic universe.
(If you had just one, it would look pretty silly calling himself father and praying to himself.)