If one were to assume that the Biblical God exists, then we can assume the first cause of his existence is irrelevant to us, because it is beyond our logical capacity, by Christian standards.
And, in relation, the Universe creating itself would not be plausible in the same way, because the Universe is a vast, perhaps infinite, mix of living and dead things that are not necessarily sentient. It's definitely, as far as I know, not one massive sentience thing. It's just a collection of things that happens to contain a few smaller sentient pieces.
But, in antipode, the Biblical God is a sentient being capable of thinking, and because of that ability, he would exist, and if he is "everything and nothing" at the same time, once again defying human logic (like lights being on and off at the same time), then he is still beyond our comprehension, so we'd never know whether he existed or not unless he proved it to us, and we'd never be able to understand the cause of his existence because everything we know is bound to concepts that we've constructed. Finite spans of life and death that always have a definite beginning and end, things to which his existence would not be bound.
I hope that made sense, lol.