1 - I'm not claiming that the standard model is the ultimate mode. I'm just claiming that following the assumption of the Big Bang which is part of the standard model, then the existence of a God before the creation of the universe is a de facto impossibility.
2 - Something that may or may not exist outside our universe, can't have any influence or even be able to observe our universe. This, is not a theory, it's the definition of Universe. Thereby, the most your could say from the Plato's cave allegory, was that a God created the cave, but that the rest of the world where that God was must have existed before he himself came to exit.