I am going to make a topsy turvy cake for my daughters first birthday this week and would like to use the method taught by Sharon Zambito in her video. I live in Florida, so my house is air-conditioned, however it is not 68-70 degrees, but closer to 78-79 degrees. If I put the cake in the fridge after I ice it with ganache, will condensation be a problem when I go to put the fondant on it? Also, I need to decorate the cake on Friday for a Saturday party. The cake is going to have to sit out overnight. Will this cause the ganache to spoil?

No it won't be a problem, I firm up my ganache in the freezer when I am in a hurry, I use sugar syrup to stick my fondant on with and wipe most of it off with a paper tower, you can do this with the condensation if you are worried about it.

I have left ganache and fondant covered cakes out of the fridge for a couple of weeks with no ill effects.

You won't need to refrigerate it unless the filling isn't shelf stable. If you do refrigerate and some condensation forms you can blot with a paper towel but you do want some moisture so that your fondant will stick to the ganache. I usually brush mine with a little water to get it to adhere well.