If doing a crumb coat, be sure you don't refrigerate the bottom layer for more than a minute or two before putting on the second layer; otherwise, it will be too cold and the ganache might solidify.
This cake is great even when made a day in advance; just be sure to let it come to room temperature before serving.
Cake boards are sold in specialty baking shops, but you can easily make your own. Just cut out a sturdy piece of cardboard in the size you need and neatly cover it completely with foil.
For a step-by-step instructional video on how to decorate the cake, watch the last step of this
Chocolate Cake recipe. Note that the video recipe shown is not a vegan-friendly recipe, so just go to the last step.