Do all the demo, plumbing and grading before you install the coping. I would install the coping last then do a final grade of your gravel base for the concrete with a hand rake. If you are worried about the concrete staining the coping when installing the concrete deck then you could lay a thin mil plastic over the coping and down the back side of the coping; then as the concrete is installed put your expansion foam in level with the back of the coping. You can cut out the plastic after you zip the top off of the expansion foam.

Hope this helps