Cupressus x leylandii
Leylandii trees part of the Cupressus family of conifers make very large trees indeed, excellent screening very tall unwanted views. They do need plenty of space to grow in. If they can be pollards to an idealheight or into a superb hedge. They are vigorous and a good choice for an evergreen conifer hedge.
How many should you plant? 3 plants per meter, but if you you buy the 10 litre pot or if planting larger specimens, including field grown root ball plants then plant just 2 per meter.
How fast do they grow? Cupressus x leylandii are the fastest growing Conifer tree, cut your hedge once a month through the summer, more regularly for topiary.
Hardiness? Frost resistant hardy plants.
Soil type? Lightly acidic, like most plants, when planting it is best to add some ericaceous purpose compost to help the hedge take.