I nearly always use just the Global Illumination and one sunlight. I do move the sun around and change the angle, it depends on what I need to illuminate. When the sun gets close to the horizon, the atmosphere gets noisy, or grainy. Increase the atmosphere samples. 64 is almost always fine, 128 is the max I would use (render times increase dramatically after 64)
When to start adding shaders to the landscape, think about how the colors/shaders layer. Rock(steep hill sides), sands, grasses, then fake stones, etc; I give each type its own surface layer. Slope controls can be used to keep the layer from overpowering the previous. I use altitude for strata color changes. Like the Grand Canyon.
Read, read, read. While you are rendering, check the docs and the forums. There is tons of information on nearly every feature of T2. Good landscaping!
