In advance: Using royal icing, make 70 tip 125 roses with tip 12 bases. Let dry. Also: Make center heart plaque. Set aside 1 oz. of white fondant; tint remainder light rose. Roll out rose fondant 1/4 in. thick. Using 6 and 8 in. pans as patterns, cut 1 fondant heart in each size. Let dry on waxed paper-covered board dusted with cornstarch. And: Make monogram. Using white and rose fondant, make 2-tone letters following mold directions. Let dry on cornstarch-dusted board. Using royal icing, attach 6 in. heart to 8 in. heart; edge hearts with tip 3 beads and let dry.
Ice 2-layer 14 in. cake smooth in buttercream, with white sides and rose top. For cake side swags, roll out remaining rose fondant 1/8 in. thick. Cut circles using cutter; cut in half with paring knife. Starting with front point of cake, attach half-circles to cake sides with buttercream, aligning straight edge with top and ending so that half-circles at front point meet. Pipe tip 46 (smooth side up) bands at swag points and at center of swag, approximately 1 1/2 in. apart, on cake sides. Pipe tip 8 ball bottom border. In royal icing, pipe tip 3 bead garlands at bottom edge and center of fondant swags; let dry. Position roses on cake top. Position heart plaque; attach monogram with fondant adhesive.