I wanted to bake in advance and freeze the undecorated cakes. If I want to be covering with ganache next Friday and fondant next Saturday, when do I defrost them? Do I do it in the fridge or on the counter?

I'm concerned about condensation or anything else that might happen if not done correctly.

I would take them out of the freezer on Thursday night and leave at room temperature to defrost, in the plastic wrap they were frozen in. Condensation will form on the plastic, not on the cake.