You won't have to struggle to keep the wine flowing, and guests can easily uncork bottles when you're busy. Have nonalcoholic alternatives available, including bottled water. Set up your coffee maker in advance. You might also have a sugar bowl, a creamer, and some cups ready, just in case guests want to change gears. There are rarely any leftovers, and abundance adds to that celebratory feeling.
People eat more in cold weather and drink more in hot weather.
For more guests one makes more food, of course. Guests at larger parties, however, generally consume fewer hors d'oeuvres per person. Dips and spreads are convenient, but finger food is more festive. Have nuts, pitted olives, and good cheese stocked in case you run low on other foods. Pass a platter or two yourself to circulate among your guests and encourage eating.