You need an insulated ground and neutral per 10-806(5) and 10-808(3). Aluminum is cheaper and easier to handle. Using oversized wire increases the required size of bonding and grounding conductors in Tables 16 and 17.
I had an instructor explain wiring above code. He said that the length of wire out of a service head is minimum 30 inches. 3 feet won't be rejected, but it isn't better. It's just a waste of money and material.
