Hi Naomi-- I'm sorry I couldn't get back to you before now.
Regarding the ganache: I generally use white chocolate ganache, but when I want a real chocolate punch, I use a mixture of semi-sweet and bitter sweet chocolate. For the white, I use two 12 oz bags of white chips to 1 (8 oz) C. heavy cream. I heat the cream in the micro to just scalding and hold it aside while I melt the chocolate in the micro, watching that it doesn't burn. Since the chips hold their shape even when melted, I do it in short bursts, stirring and checking. When melted, I quickly reheat the cream and pour it over the chocolate. I let it sit a minute then thoroughly mix it with an immersion blender until smooth. Placed aside in room temperature, it generally takes a day to firm to a peanut butter consistency. (I have rushed it a little by placing in the fridge for a short time.) Leftovers, I keep covered in the fridge. Then I can re-soften briefly in the microwave. It keeps well, refrigerated.
Applied with a small spatula and smoothed with a hot knife (dipped in hot water and wiped), it easily can cover a sculpted cake.
For the dark chocolate ganache, I use 24 oz chocolate to 12 oz heavy cream. I use the same method as for the white. (I have modified the procedure from what you'll usually see in the recipes, but it works for me.)
I have whipped ganache before, but only when using for fillings. I've not tried to cover a cake with it.
As to your fondant question, I've never had the colors bleed after refrigerating. But I won't put a fondant covered cake in the refrigerator with gumpaste decorations on it since the gumpaste would soften. Unlike some you'll read here, I don't have any trouble chilling a fondant cake. I just let it come to room temp without touching it until the condensation evaporates.
I hope this helps you as you try new things. Good luck!