plant a double staggered row with each plant in a row between one and two feet apart, or three feet if its a long hedge.
buy bare root transplants in the autumn, dont worry how tall they are, you want fibrous roots and cut the stems down to about 12" tall, this gives a good root to shoot ratio to establish them quicker, and makes them branch low down so you wont have one of those bald leggy hedges with bushiness only at the top.