Re: stepper motor rating?
4 wires means that you need a bipolar driver. If you are planning to make your own driver, you can try using L297 with 2 x L6203. It will a basic driver, but allows you to test your motor. Depanding on your application, it can be even a satisfactory one.
High voltage is desired to maintain torque at high speeds. As the voltage increases, the current in the coils can reach the desired value faster. If you try to drive a stepper motor at high speeds with low voltage supply, as the time between steps is small, the current in the coils may not reach the peak value before the next step, so the torque is reduced. But applying high voltage causes high currents which can damage the coils. To prevent this, something called "chopper" is used. It compares the current with a reference value and turns off the power if the current is outside of the limit (which is 4.7 A for your motor), so preventing coil damage. L297 has chopper feature.
What L297 can't offer is the microstepping feature, which increases the resolution of the motor and decreases the resonance problems. The costs of microstepping are the reduced torque, and a more compicated (and probably expensive) driver.
Here is L297 + L6203 schematic that I found with a Google search:
**broken link removed**