When it comes to a buttercream iced cake, which is the best way to make little decorations to stick on? I was thinking of making little mini fbct decorations but I'm worried how it would work. So would candy melt decorations do better? If so, what's the best way to apply them to the buttercream? Thanks!

Look here:
http://cakecentral.com/modules.php?name=Forums&file=viewtopic&p=6749598#6749598

Or use candy melts

Fondant cutouts stick really well to buttercream.