If you have the hardware skills (soldering, etc), then modifying the servo should be easy, minimal risk. Have you look at the tutorial link? Do you think you can do it yourself? I am sure you can.
The Arduino is just an example, the code should give you an idea how the modified servo is to be used.
Controlling 18 servos using a single microcontroller would be very difficult. You need to generate 18 PWM signals to control each servo. And you will also need another 18 analog input to read the feedback position.
This means you might need several 2-3 MCU to drive the 18 servo, plus another 'master' MCU to control the other 2-3 MCUs