Thank you for your help! I tried using the section background image option and this only allows one image. My client is going to want 2-3 rotating images on each page eventually, so that's not an option.
I also tried using Revolution Slider under the masthead and that doesn't allow me to place the slider behind the body of the page. So I'm back to selecting the multiple images in the page setup.
It there any css for just moving where the page starts below the header?