Combine crumbs and margarine, press onto bottom and sides of the 9-inch springform pan. Bake at 350 degrees F., 10 minutes. In 1 1/2-quart heavy saucepan, melt caramels with milk over low heat, stirring frequently, until smooth. Pour over crust. Top with pecans. Combine cream cheese, sugar, and vanilla, mixing at medium speed on electric mixer until well blended. Add eggs, one at a time, mixing well after each addition. Blend in chocolate, pour over pecans. Bake at 350 degrees F., 40 minutes. Loosen cake from rim of pan; cool before removing rim of pan. Chill. Garnish with whipped cream, additional chopped nuts, and maraschino cherries, if desired.