You can choose to put eggcrate down or not. I did so that my baserock would not hurt the bottom of the tank if any rock slides ever took place. You will want to put your rock in first then put the sand around it. Optionally put a small layer of sand down and then place your rocks in and then pour the rest of the sand around the rocks. I only have a Shallow sand bed so I was more worried about my rocks shifting.
You can use live rock right away if you want to. This will help cycle the tank, but you will most likely have some live rock die off. I start with baserock and cure my own into live rock, then seed it with seasoned live rock.
Thomas
