I like to use gum paste for roses. You can make them on a toothpick base instead of wire. The bottom layer can be supported by the base cake, and the upper layer of roses can rest on, and be supported by the roses underneath. They can be secured to the cake with melted white chocolate, and for that matter, a little dab of melted chocolate can help hold all the roses together. For the upper layer of roses, I would cut the toothpicks flush and use the melted chocolate, counting on the bottom ones for support. This arrangement would limit the number of holes you'd make. Gumpaste is a nasty thing to eat, but a caution re the toothpicks wouldn't hurt.
When I use melted chocolate, I find it easier to dry and cool it with a gentle blast, (that sounds like an oxymoron!), of air from a can of "canned air" like what is used for cleaning keyboards.
I hope this helps you. That is a beautiful cake.