Isn't there a huge logical hole in this "proof" of God?

There are many flaws in the first cause argument. Why does the first cause have to be supernatural? Is there even a first cause? If god needs no cause maybe the universe is just a part of a multiverse where universe spontaneously come into existence all the time, so it also needs no cause. Of course all their argument prove to be, is a god of the gaps argument, because science cannot answer this question yet, they insert 'god' to fill the gap.