Get it sized properly.
There is no good way to size a system just based on the square footage of a home. It just doesnt work that way. Reputable HVAC installers have computer programs that you have to input lots of information into to size the proper equipment and individual room needs. There are so many variables that come into play like where you are located, which way your house faces, R-values in walls and attics, window sizes and type, and the list goes on. Dont cheat yourself. Even if you have to pay a company to run your info and get you a computer readout to properly size your system. Example of improper sizing....my neighbors house was built by a contractor who went off the basis of a ton of cooling per 900 sq./ft of house space. I can tell you that unit in AC mode will short cycle. It runs for short spurts and then doesnt stay off for long til its on again. So they end up turning the t-stat down to 72 to make it feel cool inside. Because it doesnt run long means its not de-humidifying the house so you need it colder inside to feel comfortable. My unit is sized correctly and will run for long runs and stay off for long stretches and I can keep the t-stat at 77 degrees and feel comfortable because my house is low humidity. So it does pay to size a system properly. And by the way...up here in southern PA when they size a residential system it is actually designed for around 77 degrees in AC mode. Not 72 degrees. Just my opinion.