What size generator should we get for a 1000 sq feet home, fully airconditioned. Specifications: 75 KVA - 13,500 primary voltage - 120-240 V

The 75kVA - 13500 primary voltage - 120/240V sounds like the nameplate information from your utility transformer. That size transformer probably feeds several homes. Generator sizing is based off of the electrical loads that you specifically want connected, not specifically off of the square footage of your house. But IMO you would not need a generator this large for a home that size more than likely. If you want to get a pretty good idea of what size generator to buy, I suggest looking at the nameplates of the devices toy want to run and adding up the watts. But remember that wattage needs for motors can be up to twice as high for the initial few seconds that it takes the motor to get up to speed, then it will run at the normal nameplate "run" rating.