First question I have is, what will you use to put responsive background images into the backgrounds. I’m curious because I was recently looking for some way to do this and didn’t find anything. I had to settle for using https://github.com/scottjehl/picturefill which requires an tag so I had to insert the images into the content.
The way I did this was that I provided the client with the ability to upload alternate images cropped at different sizes and I built the tags dynamically.