Can I keep this leftover dough or do I have to bake it all up now?
Yes. Keep it. Bake it. Do whatever you want with it except throw it out. This is a baker's recipe so naturally, it is going to make more cookies than a standard recipe. In fact, if you bake up this whole batch of dough, it will yield roughly 6 dozen, depending on the size of your cutters. If you only need three dozen for your party, you will find that you have dough leftover.
First, if you know from the outset that you don't need many cookies, you can easily half the recipe if you can do the math. But, if you do mix up a whole recipe and you are too tired to bake one more cookie, you can keep the dough up to a week. I wrap the left over ball of dough in clear wrap and then put it in a ziplock or air tight container. I like to keep mine at room temperature but some people like to refrigerate theirs. If you refrigerate it, you will need to get it out a few hours before you are ready to bake to let it soften. The only thing that happens to day-old dough is that it sometimes gets a little dry. All you have to do is put it back in the mixer with a half stick of soft butter and mix. The salt in the butter acts as a preservative and the airtight storage keeps any bacteria from growing. You can even use your ball of dough as "starter" for your next recipe. Just break it up into the bowl before you begin adding your ingredients for your next batch. Mostly, I bake the dough the next day when I am baking but it will last up to a week if stored properly. Sometimes I am so tired that I can't bake another cookie tonight but if I have the energy, I prefer to bake up the whole batch and freeze the baked, unfrosted cookies.in a snap top container. That gives me one jump ahead of tomorrow's cookies.