In Simutrans, map rotation means map rotation, not viewport rotatation. Not exactly ideal, but the simplest solution to implement.
Buildings do have an ability to face roads, but I'm not sure which rotation corresponds to a road at what side.
It would make sense that rotation numbers followed the same "compass" as ribis. That would make 0 north. 1 would be a 90 degree clockwise rotation from north and so on.
Dims are always specified as for a 0 rotation, that is they are x and y dimensions. For odd rotations, the values would be swapped on the map. But I'm not quite sure what your asking about. When the wiki writes about ends, it's related to stations, which add an extra meaning to rotations. This meaning is illustrated.