First things first. What sort of flavour will the cake have?
There'll be a lot of hungry guests. How many layers will there be?
What colour icing will the bottom layer have?
And the middle?
And the top?
What decorations will you add?
What sort of outfit will your cake people be wearing?
What writing will be on the cake?
Will there be a surprise inside the cake?
Finally, how many sparklers should poke out the sides?