I set my ovens on 400 degrees...when they're preheated I put the cupcakes in, leave them in for 3 minutes, then turn the oven down to 350 and allow them to bake until done.
this usually creates a really nice dome.
I would just make them dipped in chocolate (white and dark) and decorate them the way truffles are decorated, like do white chocolate drizzles on the dark chocolate ones and dark chocolate drizzles on the white chocolate ones. Nothing...
My mint chocolate chip cupcake is a dark chocolate cake, with a mint chocolate chip buttercream...The buttercream has mint flavoring, and I top it with mini chocolate chips. Oh and I tint my buttercream mint green.