How much should I serve? For a party after lunchtime but before dinner, plan on seven to nine bites per person. A substantial brunch or evening meal calls for twelve to fourteen bites per person. Hint: use the scaling function on Allrecipes to size recipes up or down to suit your head count.
How many drinks? One bottle of wine serves five, while a bottle of champagne serves about six (champagne glasses are generally smaller). A gallon of punch yields approximately 30 servings of five ounces each. Be sure to stock non-alcohol choices, and brew coffee and tea as well.
Can showers be potluck? Yes, unless the party is very formal. But this is one time when you don't want to leave things up to chance. Do give menu suggestions and keep track of who is bringing what.
Other things to consider. Study the guest list and the menu to calculate the plates, utensils, glasses, cups, serving pieces, and linens you'll need. Think about how to keep hot things hot and cold things cold. Is this a sit-down affair (you'll need tables and chairs) or will guests eat on their feet? Plan your menu accordingly, and rent or borrow the equipment you need.