You didn't say what you're using it for, or why you settled on this particular motor, but if you're making a router to work with wood, I'd call it a bad choice. Wood needs to be cut fairly quickly, or it starts to show dwell marks, and will burn in extreme cases. With a gear-motor, you're trading speed for torque. But since steppers have less torque the faster they try to run, this is an exercise in futility. (Servo motors, which tend to perform best at higher speeds, are better candidates for gear-heads.) The torque curve PDF is missing for that motor, but you can look at torque curves for other steppers and get the idea. Also, at 4.5mH inductance, it really wants about 68v DC to run optimally. Most inexpensive drivers won't be able to handle that much voltage. I'd say keep looking, but build the frame of your machine in the meantime; once it's done you'll have a better idea of how much torque you really need.