Welcome to the forum Carl.   I’ll have a go at answering the question after lunch, if someone else doesn’t get in first!

Dave

Agree with Robert.

The motors connect direct to the shield.  However, you will also need a separate 12V supply to power the motors and Arduino.   Could be done with 12V 1A wall wart but I’d go for 2 or 3A to make sure the motors don’t brown-out the Arduino.    The supply can plug into the Arduino’s power socket. (Other options described on the Adafruit website.)

Max speed depends on how many steps or micro-steps the driver delivers and on the physical characteristics of the stepper motor; they are not intended to run fast!

Your choice steps in units of 1.8°, or 200 steps per rotation, possibly allowing up to about 1000 rpm max, though 500 or 600 rpm is more sensible.    Micro-stepping increases positional accuracy but reduces RPM, so 800 micro-steps per rotation would deliver 150rpm.

Running steppers at high-speed isn’t recommended because doing so loses positional accuracy and torque.   Not good because the purpose of a stepper is to put the spindle in the right place at the right time, and that’s unlikely to happen if the motor is over-sped.  That’s why 500-600 rpm is recommended as more sensible.   The motor has a chance of achieving that speed without losing skipping steps.

Dave