Ans: Use the zipped executables at following URL to change the address.
(Use LEGO firmware 1.29 or higher for this, and follow instructions to install.)
Explorer.zip upon installation, attach sensor to port 1, run the program and follow on screen instructions.
Ans: 8-Servo controller uses universal connectors, Actually it has only male header so ideally it is compatible with all of them. You will need the external power supply from range 6-8 volts depending on your servo.
Ans: Yes, all the 8 motors have separate position control and you can control each motor position individually.
Ans: Yes, you can. Ensure that your each NXTServo has unique I2C address.