An interesting router design, I've never seen one like it. Please post pictures as you build the machine.
If I have a choice, I will always go with a servo system. I think your motor choices will have plenty of power to do what you want. Maybe using a 2:1 timing belt reduction will insure that you have enough torque, without sacrificing speed. Stepper motors are rated at holding torque, which drops off rapidly as the speed increases. DC or BLDC servo motors are rated at maximum torque and have a more flat torque curve over the operating range.