Now as for alcohol per guest: You should generally allow for two drinks per hour per person during the drinks reception and one drink per hour from then on. Always order 10-15% extra so that no matter what, you don't run out of alcohol.
Breaking Down the Calculations As a general rule of thumb, plan to serve one drink per guest per hour of reception. In other words, if you're having a four-hour reception with 100 guests, provide 400 servings of alcohol. Full bars typically offer beer, wine, and liquor.