What cakes pans should I use to make a pair of dice? Also, most cakes I've seen use fondant... I've only used it once and my cake was "lumpy". How do I avoid that?
how many people are you trying to serve with the dice?
I would think 4" squares would work. Just use two layers in each cake so that the cake is 4" tall (or a little higher)
If you need more servings than the two dice will serve can always set them on another cake or have cupcakes.
As for the fondant, did you put a layer of buttercream underneath of it? (or ganache can be used too) If you put it right on the cake it is harder to get it smooth (and stick too)
btw.. welcome to CC
since dice have very straight edges, you can cut fondant squaresto cover the faces of the die moisten the edges to ge a good seal, the trim if needed, make sure you put a good finish coat of frosting before putting on the faces