You would need specific information about the insulation values and ductwork of the home. 20 years ago, homes were built with R-13 (3-inch) batt insulation for the walls and R-22 (6-inch) fiberglass insulation in the attic. With the windows you describe, usually double-pane, your window sizes are not excessive. This translates to approximately 1-ton per 1000 sqft. At present I am sitting in an 1100 sqft home being cooled by a 1-ton ductless split unit; my former cooling unit was a 10,000 btuh window unit which I eliminated to achieve quiet once more. My 2-ton heat pump before that ran less than half-time in the summer.
A new home is insulated to higher values and requires even less cooling; but this does not mean that you only need a 2-ton unit. Other factors come into the design of a home cooling unit. If you plan to entertain many people during the day, each person needs an additional 800 btuh beyond the heat leaking into the house from the outdoors. Also, air conditioniing ductwork needs to deliver more air upstairs than down. Heating ductwork delivers more air down than up; so there are ductwork considerations that are often unresolved as a source of discomfort.
I have taught heat loss and gain courses for over 30 years - many supply houses, fuel companies and contractors use my software. If you can not find a local contractor or supplier to calculate your cooling load, give the dimensions of the house, the window sizes and the insulation thicknesses in the ceiling, walls and floor and send them to me. I will calculate the heat gain. You can find a form to download at my web site: http://www.hydronic.net or "Hydronic Network"
There are also instructions there on what to look for when doing an air conditioning estimate and air conditioning a home.