About 1000 kWh per month or 12,000 kWh per year

About 4 million kWh per year for a machine with a 1.5 MW capacity at a good wind site, or enough energy for about 330 typical households in Oregon.

About $2 million installed (less when installed in larger wind farms)

Between about $3,000 (very small) and $40,000 (10 kW, 22 feet diameter rotor) depending upon size, tower height, etc.

Wind farms: the large wind turbines you see in wind farms take about 0.5 acres including all the access roads and area around the tower for the transformer. A typical farmer can use all the surrounding land as before and often benefits from improved roads.
 
For a home or farm system: it depends on the tower. A tilt-up with guy wires needs more space than a tubular tower. The guy radius must be one-half to three-quarters of the tower height.

As a general guide for Oregon, a wind speed at hub height needs to be in the range of 14-15 mph averaged over a year for a system to approach economic feasibility. Economic feasibility also depends on the rate one gets for the energy sold to the utility (or avoided cost of energy with net-metering*), the cost of the wind system, maintenance costs, etc.
 
Of course, if one lives far from the utility grid, these numbers are completely different. The wind turbine cost is sometimes compared to the cost of extending a utility’s distribution line.
 
*Net metering: a metering arrangement with a utility that measures the difference between the electricity supplied by the utility and the electricity generated and fed back by a customer who is capable of generating electricity through wind, solar, etc.

A typical machine starts rotating when the wind speed is around 7 to 8 miles per hour (but there is very little energy in the wind at that wind speed). It will reach the full rated capacity when the wind speed is in the range of 25 to 30 mph.

Basically, there are two types of wind turbines: the constant speed machines and the variable speed machines.
 
Just like the name says, the constant speed machines do not vary the rotational speed when the wind speed increases. The electrical generator is “locked” on to the grid frequency of 60 hertz.
 
The variable speed machines let the rotational speed increase with increasing wind speed. These machines are more efficient in catching the energy in the wind. The turbine’s variable frequency alternating power is then “transformed” into constant frequency power to be connected to the grid. Optimum efficiency, in terms of catching the energy in the wind by a typical 3-bladed wind turbine, occurs when the blade tip speed is about 5 to 6 times the wind speed. That’s why the large machines have a slower rotational speed, while the tip speed maintains that optimal ratio with the wind speed.

Some do, others are fixed, it depends on the control philosophy of the wind turbine.        

Small systems for home and farms may have blades as short as a few feet to about 10 or 15 feet. Towers should be at least 30 feet higher than obstacles within a radius of about 900 feet.
 
Large wind turbines for commercial wind farms have towers 200 to 360 feet tall (60 to 110 meters), with blades as long as 130 to 200 feet (40 to 60 meters). The large wind turbines in Oregon are in the lower range of the size noted above.
The very large turbines are primarily being developed for the off-shore market in Europe. The largest generators being tested in Europe are now in the 6 MW range.

 The most important reason is the stability of the turbine. Windpower.org  contains more detailed information and an overview of how wind power works.