Generally cupcakes are made 24 hours prior to the event. They really don't keep well like cake, even if you completely cover them and seal in the cake with buttercream or fondant.
Cakes last better on the counter because they have been completely covered with buttercream or fondant or ganache which acts just like plastic wrap to "seal in" freshness.
A solution may be to bake all your cupcakes and FREEZE them.
Make all your fondant/gum paste decorations way ahead of time (weeks or months) and store them in a NON-airtight, cardboard box.
Make your buttercream and FREEZE it.
Stage your working area the night before, take everything out to thaw (or thaw in refrigerator then a couple of hours on counter in morning). Assemble everything.
If you haven't frozen cupcakes/buttercream before, try it out with a sample batch and see what you think.
p.s. NEVER put fondant decos on top of whipped cream icing. It will melt into a gooey, ugly mess.