I lit some green screen shots last year, and typically you want to give your subject a backlight to help cancel out reflected green that could be a problem in compositing. In terms of the limited space, I'd say try to take advantage of the "inverse square" rule. If you use lower output lights closer to your actor, it will cast less light on the backdrop than if you had a stronger source farther away. Softer sources will also cast less shadows, but the farther away they are the harder the shadows too. As an extreme example, the moon is reflected light, but acts as a point source because it's so far away.
If you have wide shots where you show the entire actor, that's a whole different animal, and I don't really know the answer.