I would agree in buying the black fondant. If you are using buttercream, start with chocolate and add your black. You will need much less black and you wont have the problem of the taste of too much food dye.
Black and white is the most difficult combination to work with. My advice is to keep a super clean work space and wear gloves if possible and change them frequently when working with black. Using the bling ribbon is a great idea. I would use it as a trim on the cake board or on a separator tier, not on the actual cake since it is not edible. For a really simple black and white bling cake, take a look at my photos and you will see one with a big black fondant bow. My last bit of advice, make sure you sketch out your design before you start.
Roseann, Long Island, http://www.TheDecoratedDessert.com
