you don’t have to be original (especially in a very niche place like this), it’s more on the execution of the concept. also I only know of one game (Fats Food) where you run a restaurant so there’s that.
balancing difficulty I can see being hard if you can only raise the difficulty by having the player do stuff faster and longer. maybe having different cakes having different ways of being made is an option and have interesting combinations of cakes, demand speed and duration or something