No matter how you slice it, you can't get more than THREE (3) spatial dimensions!!! You can use many "dimensions" in a vector to "represent" something in reality but that's all it is: just a representation and NOT reality.
When it comes to Big Bang, I am a non-believer.
Sorry, but that's just silly. You're essentially taking the view that if you can't imagine it, it cannot be. If nothing else, try to imagine a God's-eye view of eternity, and you'll get a vague idea of how that 4th spatial dimension would work -- seriously: how to you think God sees the universe? To be God, He's got to be outside of the three-D + time we've got....