I will respond about the ganache. It can be refrigerated for a few days, as long as it is at room temp when you put it on the cake. It has to be at spreadable consistency. I would say do not worry about it. You are not talking a week or weeks, just three days. Just put it in a bowl and cover w/ tight plastic or simply air tight. If you can make it two days before assembling the cake , it should be good. I have not made mud cake, but I would think store it like any other cake. In the fridge tightly covered w/ plastic wrap. After filling and decorating, refrigerate w/out the plastic cover wrap. Good luck and let us know.
I think this reply is late. I’m sorry.