I always start about a week ahead mixing up my cookie dough. I place it in food storage bags and write on the bags the type of dough.
You will need to decide how many cookies of each kind each person will take home. I would suggest at least 1 to 2 dozen of each. You will also have to decide how large you are going to make your cookies. I like to make mine small for cookie trays. I usually double the yield of a batch since I make my cookies about half the size I would normally. Then you will need to calculate how many batches of each you will need to mix up. Even though we made 28 kinds the last time, I think we mixed up over 60 batches.
This is a good time to ask others to help mix up some of the dough.
You will also want to make sure that you have all the ingredients you will need for finishing the cookies, such as icing, sprinkles, melting chocolate, coconut, etc.