sparkly: are the flowers going to be prepared in advance from icing, allowed to dry, then placed on the cake in their hardened form? Or are the flowers going to be prepared and placed immediately on the cake (still 'wet')?
If the flowers are going to be hardened, icing type may not matter since they'll be too hard to eat anyway.
If they'll be soft enough to eat, vanilla buttercream icing is great. If you don't mix it yourself, some bakeries will sell you their aerated buttercream.
That's what I have to offer