I'm doing a wedding cake in September and am going to order Satin Ice to cover the cake in since I want it to be a nice white! It'll be a round double layer (about 4" each tier).. Three tiers, 10", 8", and 6".. Can anyone tell me the approximate weight I'll need to order? I'll also be doing a ball border around it. I don't want to have too little or too much (because it's way too expensive). Thank you for the help!