We have used the green cymbidium orchids as the cake topper. Each flowers are inserted into the internal water source to ensure they stay hydrated. Many junior bakers and florist just poke flower directly into the cake. I usually recommend people not to do that, because it damages both the flowers and the cake.
To repeat the crystal elements, we have scattered diamond confetti on the cake table, and use a crystal cake knife and server set (these are available for rental at Secrets Floral).