You need enough to feed people, enough that nobody is hungry, and enough to soak up the copious amounts of booze being consumed. Too much and you run the risk of food coma-ing the party.

One of my cousins went all out on food, tons of stations, lots of rich food, and nobody could get up to dance, and the drinking was subdued to hell, spent 3 hours in my bed clutching my gut and my wife was hoping she'd just throw up. Next day reporting from all sources was heartburn, indigestion, etc..