You should try to book your caterer at least 6-12 months in advance of your event. Ask them about their experience, background, and culinary education. A good rule of thumb is of pound of ice per guest. You may need extra ice in really hot weather. There are many details to consider such as tables, and chairs, plates, napkins, table linens, chaffers, glassware, sternos, silverware, serving pieces, tents, etc.
Some people choose to use plastic flatware and paper plates in order to save money.
There are many different grades of silverware, tableware, glassware, etc, and different colors of linens to choose from. You need to make some choices and find out the price differences for your rentals. Your caterer can help you figure out what items that you need to rent. Most caterers charge you for rental equipment. Some caterers include the cost of rentals along with their food prices per guest.