The best course to follow is to hire a professional bar tending company like Black Tie Events or Pourmasters. All their bartenders have TIPS Alcohol Certification and the Arizona Food Handlers Card. I know these companies personally and can highly recommend their services be it just bar tending, complete bar services or just to sell you the liquor.
But if you are sure you don't need outside services, I have found a nifty little calculator to give you a rough idea about the amount of liquor you should buy for a wedding. I found it on one of my favorite sites REAL SIMPLE. They have set it up by time of day, number of guests and whether you are serving a full bar or just wine, beer and champaign. You can find it here and may your wedding be joyous and safe.