My daughter would like this design for her wedding cake and I'm wondering if you all think this is a fondant covered cake with the fondant/gumpaste cutouts added, or buttercream with fondant/gumpaste cutouts attached? Any tips would also be greatly appreciated!

Silicone molds maybe?

To me it looks like the cake is covered in white fondant and then ivory gum paste flowers and leaves are attached. The gum paste flowers and leaves look like they have some royal icing details on them.

Beautiful cake. Good Luck

Cake can be either fondant or buttercream. Won't really matter.