Well I can't tell what size those flowers are from the picture either but what I would do is to get out my drop flower tips and see which size I like best......as far as the side of the cake, I think there is just a top border and a bottom border with nothing in the middle, you could cluster very small drop flowers and leaves at even spaces in the middle though if you wanted. Hope this helps.
I found it for you...your original post on this
I think it would look pretty with a couple of different sizes of drop flowers. I would try some in various sizes and use the ones that seem to fit best.
very pretty cake!!