This cake was made using 3" styrofoam cake dummies in between the tiers. I painted all the flowers with an airbrush ahead of arranging them. The flowers we stuck in if they had wire, but most were "glued" in place with royal icing. My advice here is use as many different size flowers as you can so that you don't have blank spaces. I have been known to make a few roses petals and squeeze them in when the are soft so it looks very full. We also airbrushed the dickens out of this cake when it was all stacked and ready to go! My bride wanted a pearl finish so she got it!
Anytime you have a tier of cake floating above flowers you have to deal with hiding the edges of the cake boards. For me, ribbon is the answer because it is not heavy and you can pull it tight so it doesn't sag. Buttercream borders can fall off due to gravity, as can fondant pearl borders if they are large. Have you ever noticed that when the bakers in Europe make this type of cake, they still have a larger cake board under each tier? So a 6" cake would have an 8" cake board, then a 10" cake and 12" board, etc. I don't like the look myself, but it sure would be easier!
*I owe you a close up picture. I accidently deleted it :(