In regards to the bonding strap in the subpanel, I've read the following: 1) don't use it in the subpanel, 2) always use it and 3) only use it if it's used in the main panel. So which is it? I've separated neutral and ground in the subpanel, so I see no reason why I would need it.
And as far as bringing the #6 bare copper wire from the ground rods, how do I physically bring them into the box. I can't imagine I have to use a clamp through a knock-out. Can I just drill a hole in the side of the box to bring the wire into the grounding bar? If not, how am I supposed to do it - I can't find any specific information on that aspect of the grounding wire.