Stepper vs servo
I'll step in here a bit.
Just having GPIO is not enough to control a stepper mechanism. You will need a interface to control the windings via the GPIO for single-axis steppers. Your handler must control the interface to control the step direction and rate for a stepper. Many manufactures provide controller chips/controllers that will make things easier for a stepper using single-axis control.
Where a servo mechanism has the motor, control interface(include feed back circuitry) to control motion speed and direction since the servo will be 3 wire. Thus isolation technique should be used, not directly driven. GPIO control for a servo is different and generally easier. Your handler will be simplified for a servo system by uses of a register technique. If you use a gated local register then you can buffer the control bits. In this manner your handler will provide control techniques that will enable the feedback mechanism to be read via interrupt thus positive(continuous)Input/ Output control.
One must know the advantages for a stepper based system (torque) over a finite servo mechanism. Stepper systems are costly at higher torque at the expense of power. Smaller and proportional control with a servo mechanism is very doable. As you increase size for servo mechanism(s) then one must compare between the two types of designs. What you are driving or managing will generally dictate the design.
Plus you need to remember to consider the angle when using a stepper vs servo. Type of controller for each will dictate that measure. How finite the design control will be for control of the drive function.
So if I were to suggest anything, I would experiment with both a stepper based system and a servo based. You will need to keep the load low so you have a fair comparison between the two control techniques. From a experimental sense you will need to have decent monitoring equipment. Been there done that many times!
I know your topic is 'servo' but you really should compare the two techniques. That way the advantages or disadvantages for each can be learned. Real world experimentation will reinforce your theoretical experiences.