Because of divine simplicity, the absolute maximum of perfection logically excludes the possibility of more than one.
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.
Couldn't you suppose these gods had the same one-many property as the Trinity and say that it's whole essence is perfect?
If you need a god to explain where the universe came from, induction would like a word with you
My understanding of God is not “one more thing in the universe that explains an earlier thing.” It is closer to God as the ground of being itself: the reason anything exists at all, including matter, energy, spacetime, causality, and whatever laws describe them.
Then explain evil