In short: Calculate the torques involved. Look at the speed/torque graphs for candidate motors.
Torque is needed for three reasons, to overcome inertia as the wheel speeds up or slows down, and to
give power to the load and to overcome friction.
You've said nothing about the load, but a back-of-the-envelope calculation suggests the moment-of-inertia
(MoI) of the wheel will be about 1.0 kg-m^2 (using formula for MoI of solid disk radius 0.2m and 25kg mass).
The friction depends on the bearings principally.
The eccentricity of the mass on the wheel will also create a load.
But the actual load is presumably due to decoiling (and may be negative if the motor has to resist pulling?)
Any reason why a stepper is selected for this task?