You should add the second hive body or super when the majority of the frames in the first hive body are fully drawn out, (8 or 9 frames). A second super should be added after the first super is about one half full.
If you are in the city, you should put the entrance of the hive facing a high fence. This will force the bees to fly in a high flight pattern, avoiding neighbors. It is good to give the hives a wind break to protect them. You can also place the entrance facing the sun to allow the bees an early start in the morning. The hive can also be placed on a hive stand, concrete blocks or a wooden pallet to keep it off of the ground.