I have been asked to make this cake by a bride who wants all buttercream. I told her I believe the flowers and leaves will have to be fondant. How should I go about making the flowers and leaves? All fondant? Part gumpaste? do I make them ahead and let them dry on cake dummies?

I made my son's wedding cake .... all BC; BC 'stem' going down the length of the cake; fondant leaves on the stems. See pic in my photos (whtie cake with black stems/leaves .... I think it's the first pic).

What kind of flowers? Many flowers can be made with buttercream with great results.

Wish we could see a pic. Some flowers can be made with all fondant and some need a little extra firmness to hold their shape. Same for your drying technique. It depends on the shape you want them to hold. I have used styrofoam egg crates(the one you get when you buy large crates of eggs) to dry large amounts of petal flowers and daisies. Other flower like lilies would obvious need a different technique, but yes I dry before hand.

If the bride wants the bc flowers there are so many that turn out stunning in bc!! There are some great guides on YouTube for making bc flowers. If you have a photo we can tell you if they will be better in fondant, bc, or a fondant/gumpaste mix etc.