don't forget "French Dips"...that being said, 8 oz. (by weight) total, per "teenage" guest should be plenty, even for those ravenous appetites. In other words, if you have 12 dips and 30 guests, that's about 1 and 1/2 lb. of each dip, and so on, to include:
"Classics" (boring, but people will be confused unless you have them)French Onion
Salsas (up to three)
That's seven right there!