I have a request for a Minnie Mouse and Mickey Mouse cake for a friend of mine. She is expecting about 20 guests. If I did a 10 inch round for the face and 6 inch rounds for the ears (x2), do you think that would be enough cake to serve everyone? Thanks for your advice!

Two single layer 6" and one single layer 10" will yield you at least 23 servings, so that would be perfect. Double layers would make way, way more than you need.