I heard the area generatable is 4 time larger than the equivalent area on earth that is possible to geenerate.
He uses procedural Terrain generation, so there is not limit. New parts / revisited will be generated on the fly. I guess he only saves blocks/elements that where altered after the terrain generation procedure, this limits the amount of data that has to be saved.
To have the same block-elumination in gamestudio, you would need to be able to alter each of the 6 block sides brightness seperately.