Your master ambient light can be either 200%+ intensity or -200%, depends on whether you want to isolate the subjects from the surroundings or give the viewer scene details to amble through. And it really doesn't matter whether it's infinite, point, or a 135 degree spot, as long as it lights the scene.

Backgrounds either play a role or they simply frame the subjects you're bringing out through lighting.

Some say shaders make the figure, and most tutorials here at Renderosity say that postwork does all the job. Imo, if you learn the shaders well enough to apply them, you'll have a render that just can't be improved with postwork, though you may put stylistic emphasis on it.