My son is purchasing a house in Atlanta. The upstairs is finished but is only served by a single register from the downstairs furnace(gas) and air conditioner, as well as a window air conditioner. The approximate square footage is about 250 square feet including a small bathroom. The plan is to enlarge this are in a few years to a master suite approximating 350 square feet. We are considering adding a new unit upstairs in an area that would not be included in the renovation. Would it be best to wait a few years until the renovation, have prelimanary plans drawn now for correct sizing or estimate total square feet now. Would a heat pump be appropriate for this area? Atlanta has relatively mild winters and hot, humid summers. Thanks for your help.