Preheat oven to 300 degrees F. Combine crumbs, sugar and margarine; press firmly on bottom of 9-inch springform pan. Reserve 10 caramels. In heavy saucepan, combine remaining caramels and 1/2 cup half-and-half. Over medium-low heat, cook and stir until melted and smooth. Stir in chopped pecans. Spread over prepared crust. Bake 15 minutes. Meanwhile in large mixer bowl, beat cream cheese until fluffy. Gradually beat in sweetened condensed milk until smooth. Add eggs and vanilla; mix well. Pour into prepared pan. Bake 1 hour or until set (center will be slightly soft). Cool. In small saucepan, over low heat, cook and stir reserved caramels with remaining 3 tablespoons half-and-half until melted and smooth. Immediately spread over cake. Garnish with pecan halves. Chill thoroughly. Refrigerate leftovers.