I make wedding cakes up to 2 weeks in advance (no more than!!) I ice it in 2 stages- slice through the middle and fill with buttercream and let it sit overnight, thin layer of buttercream then straight on with the sugarpaste!
Sponge cakes last better than people give them credit for! Though bare in mind wedding cakes tend to be a lot heftier than birthday cakes so hold their moisture better. As long as there's no milk or cream in the icing it doesn't want to go in the fridge.
Sorry if that's a bit garbled! I've got one eye on here and one eye on Neighbours catch up!!