first things first. what load does your motor have to move? at what speeds?
knowing the above two pieces of information is most important in being able to correctly work out the rest problem. The load will tell you peak torque, which is directly proportional to current, and later will tell you two things. The first is power output, which is equal to torque by speed (with a bit of a constant), and the second is inertia (with a bit of modelling of your actual load)
Inertia can be a bit of a gotcha is these situations. If you think that the motor has enough torque and power handle the load, you may find you have problems in trying to "control" the load. With more inertia on the load, it will take the motor sometime to ramp up, and the load will continue to drive the motor, on the other hand, having too much inertia in the motors rotor will mean the motor responds slower than needed for the given load. Ideally these need to be matched by circa 10:1 in the motors favour. dont forget that inertia scales by the square of the gearbox ratio!
back to your problem, if you are not interested in precise control, consider, but do not worry about the inertia issues.
What you do need to answer is the questions about your load, speed and gearbox being used.
With the extra information, it will be possible to answer your question about matching the amplifier to the motor!