Hi!
You're right about passes/layer... it doesn't make much sense for example to calculate all the texture because you just changed the lighning. And tuning in an compositing app or photoshop makes much more fun
I'll make a wireframe as soon as I'm back at my workstation... Basically the scene consist of just some basic bevel boxes (polys). The edge pass helps to break lines. And of course it renders extremly fast.
Before I began to extensivly use compositing I did most of my work directly in Maya (if it's CG). Now I use Maya as some kind of better "sketch tool".
-Klaus