For a wedding cake do I only charge my charge per slice multiplied by number of guests( or slices) and is that my total? Or are there other charges that are typically added in after the cost per slice multiplied by slices?

add in any extras like gumpaste flowers..Delivery/setup fee...internal supports like pillars etc just in case it is not returned.The more embellishments you add the more money you charge over above the serving price.