Trinity vs. Oneness

In the beginning God Created the heavens and the earth... And the Spirit of God was hovering over the face of the waters...Then God said, "Let US make man in our image, after our likeness"...So God created man in His own image, in the image of God He created Him; male and female He created them.(excepts from Genesis)

Questions to consider:
1) The bible never tries to prove that there is a God, It just assumes that He is. Why?
2) Why is the Hebrew word Elohim, Plural instead of singular?
3) When Moses says the Spirit of God was hovering, what did he mean? Was it God or was it His Spirit, and are these the same or different?
4) Who is the "US & Our" in creating man? Only God creates, not angels. The bible says man was made in the image of God, not in the image of angels?
5) In Hebrew literature if one wants to put emphases on a subject it's mentioned twice. Moses mentions that man was created in God's image twice and three times that man was created...why?

It's helpful to have some kind of grasp on the Godhead in these verses. In the next (Trinity vs. Oneness) post we will look more in-depth into these verse and a hand full of others in the Old Testament before we move of to the New Testament.