Rendering an animation onto a still background?

Hey everyone!
I need some guidance regarding the topic. I successfully modeled a metal roof panel onto a plane and figured out how to render the image to only show the model and the models shadow but NOT the plane.

I want to take it a step further and animate the panel rotating like a car would in a showcase room.

Here are the 2 issues I cannot figure out.

  1. I need to show a background image into the animation. (The camera will not move)
  2. When I render an animation, it renders the 1st layer (object) then the 2nd layer (floor and shadow). when I go to combine all my PNG’s into the video editor, it only shows the 2nd layer (i guess the 1st layer was overridden).
    I have researched and played around for the whole day, but cannot find any help.

Let me know if I can shed some light on anything. (See sample attached)