I am aware that only one composite node is possible per scene with unlimited scenes per blend file but I was told that it’s possible to assign composite nodes from one scene to the next or even assign composite nodes from one scene to a specific object contained in a separate scene. For example I need to use a node to blur between objects in a scene and at the same time use a separate node from a separate scene to effect the objects in the first scene. Basically I want to stack composites.
On your Render Layer input, there is a popup selector for the scene that provides the render layer. Just set up multiple inputs for each scene’s render.
I haven’t tried this yet, but I saw it in a tutorial and plan to use it.
For Greenscreening, check out Blend That Film.http://www.youtube.com/watch?v=RbF0VL5FNsg