Most of Dunkin’s 7,800 US shops look alike, but they’re owned by about 1,000 franchisees who pay fees each month to their franchisor, Canton-based Dunkin’ Brands. Cafua’s Portuguese parents bought their first shop when he was 5, standing him atop two milk crates so he could reach the cash register. Today, the family’s empire encompasses nearly 300 stores, with another 50-plus in development or under agreement, making it the nation’s largest privately held Dunkin’ franchisee network. (Roughly 500 Dunkin’ outlets in gas stations are owned and operated by Hess, a publicly traded corporation.)