As for the lighting question:

Shadow maps are individual to each light. You can't add them together for several lights. The shadow map size defines the resolution of the shadows for that particular light. You can have one light with a map size of 1024, giving a very sharp and precise shadow, together with another light with a map size of 256, giving a fuzzy shadow, in the same scene. The shadows from each light will be different according to the map size.