Typically you can run a stepper driver with two or three pins (direction, step and enable if you need it). The driver determines the size of stepper you can control, the Arduino doesn't care.
So any Arduino can drive five motors, but you likely need the ability to home each stepper and possibly some other pins to detect problems. If you have encoders, again you'll need more pins and processing power.
The most serious aspect though is safety - if you're going to drive an industrial welding robot with code you wrote yourself, are you going to have liability concerns?