Yes. There ARE charts you use, i.e. 1/4# per person for this or that, your recipes tell you how many servings, too or at least you should be able to guess pretty closely.
Here's the deal........when you have MULTIPLE dishes, you can count on people not eating full portions of everything. The type of finger foods matter too, because if they are more of the meatball or quiche type, they are more filling than some others. Make SURE you have plenty of variety. The more things you can make ahead THE BETTER!
If I had a bit more info, I could help you out a bit more. Call me if you want. Let me know. I've had TONS of experience w/ this.