No Christian that I know of has ever claimed that God "created himself out of nothing". The Christian position would be that God has always existed. He then created a world in which there are certain rules or laws that govern it. The laws which we observe in this world don't apply to God like they do to us. God is over and above and outside of the physical laws that govern our existence. Just because we observe nature and see that things don't just pop into being doesn't mean that the same rules that prevent this from happening also apply to the Creator. The fact that I cannot understand everything about God and can't wrap my mind around how God could have always been in existence doesn't scare me. If there is a truly omnipotent, all powerful, all knowing Creator such as the God described in the Bible then it would follow that there will be many things about him that I am unable to comprehend.

I don't know what "living life as though it were meaningless would look like" and since you are the one that posed the question, I'm assuming you don't either. Perhaps the reason we can't even visualize this is because no one who's ever lived has truly lived as if life were meaningless, and in my opinion that is even more evidence that we were created by God. The concepts of meaning and purpose are so deep inside of us that we cannot even fathom someone taking an atheist at his word and genuinely living as if we are all here by chance and nothing that we do matters in the slightest. You and I both think "everybody makes their own 'meaning' in life" and I think it is more plausible to assume that we do that because that is the way God made us because if we are just a product of chance and evolutionary processes then the concepts of love and honesty and fairness do not matter and we should only be concerned with our own survival.