Prepare tiers: Trim layers. On corresponding-size foam boards, fill with buttercream to make 4-inch-high tiers. Coat thinly with buttercream to seal in crumbs. Refrigerate at least 1 hour and up to 1 day.
Cover tiers: Roll fondant (see note above for amounts) into a small disk on clean work surface lightly dusted with cornstarch. Dip the end of a toothpick into pink food coloring, and press into fondant. Repeat to create a random pattern of pink marks on fondant. Fold edges toward center; knead 3 or 4 turns. Roll out fondant until 1/8 inch thick and large enough to cover largest tier (marbling will be visible). Drape fondant over a rolling pin; center and place it on the tier. Starting at the top, smooth fondant onto cake with your hands. Cut away excess with a pastry wheel. Repeat to cover remaining tiers.
Assemble tiers: Place largest tier on cake board. Insert 12 dowels, 10 in an oval about 2 1/2 inches from edge, and 2 evenly spaced in the center. Center and place 13-inch tier on top. Insert 10 dowels, 8 about 2 1/2 inches from edge and 2 evenly spaced in the center. Center and place 10 3/4-inch tier on top. Insert remaining 6 dowels in an oval about 2 1/2 inches from edge.
Decorate tiers: On a work surface dusted with cocoa powder, knead modeling chocolate until pliable. For each tier, roll a band about 2 1/2 inches wide and long enough to go halfway around tier. Using a pizza cutter, trim bottom edge to be straight. Trim top edge with a scallop cutter to make band 1 1/2 inches high at scallops' peaks (scraps can be reused). Use a damp pastry brush to moisten bottom edge of fondant-covered tier. Working quickly and carefully, lift band, and attach it to side of tier, placing cut ends at sides of cake. Repeat with more chocolate to make a band for other side. To make band for cake board, roll out another long band, and trim to be about 3/4 inch wide. Cut away top edge using scallop cutter. Use damp pastry brush to moisten area where cake board meets edge of bottom tier. Working quickly, lift prepared band and press it onto cake board.
Tint 1/2 cup royal icing brown; transfer to a pastry bag fitted with a coupler and an Ateco number 3 round tip. Pipe dots about 3/8 inch apart around tiers' bottom edges. Use dots of icing to attach desired brown ribbon to chocolate bands, and bows to ribbon (we wrapped 1/2-inch center-stitched brown grosgrain ribbon around chocolate bands, and used 7-millimeter brown silk ribbon for bows).
To serve, spoon 2 tablespoons caramel sauce onto each plate; top with a slice of cake.
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