just add cocoa powder to your buttercream to make it chocolate buttercream. this is the recipe i’ve used in the past and if i want it more chocolatey, i just reduce the sugar and increase the coca powder until it tastes like i want it to.
Chocolate Buttercream Icing
i don’t believe the recipe will change, you’ll simply adjust the baking time to match cupcakes instead of a larger cake.
this is an excellent chart to calculate baking pan conversions and baking times - Party Cake Baking Time and Batter Amounts - 2 in. Deep Pans
YAY!! i knew you could do it!!! good job, girlfriend!! 
yup, you can prepare figures in advance and store in an airtight container. you can paint the figures, tint the fondant, flavor it, whatever you want!
the fondant will not crack, however, i would not advise placing the fondant on the cake in advance. you cannot put fondant-covered cake in the fridge. moisture will form on it and it will ruin the look of the fondant. cover the cake with fondant the day it is being served and once its done, place it in a cool place in your house, but not the fridge.
this is a great fondant Q&A site- Decorating with Fondant, How To Decorate Cakes with Fondant Icing, Decorating Cakes with Fondant Questions and Answers
incidentally, this lady Peg W is the one who gave me her MMF recipe first and was very helpful over email with my 1001 questions about it!