Staging isn't particularly hard, but is certainly a fun and exciting challenge. The key things to focus on are safety and reliability.
For safety, I suggest you employ more sophistication than a simple timer activated by a g-switch or break-wire. Using an accelerometer altimeter like an AIM Xtra, Raven, or Telemega will permit you to use a few safety features such as altitude lockouts, tilt lockouts, velocity lockouts, or any combination thereof. For example, my 2 stage flight yesterday would only stage if the Raven sensed burnout and the rocket was greater than 400' in altitude after a 1 second coast. This ensures that the rocket is substantially high in the air and eliminates ignition in the case of a CATO or instability. Furthermore you can employ a Telemega to lockout your rocket based on a severe tilt angle, eliminating waiver cylinder concerns.
By reliability, I primarily mean 2nd stage ignition. Seeing as you're from Australia, you're probably flying commercial motors. Using CTI motors that use an ignition augmentation pellet will greatly simplify igniting the second stage motor. Using Aerotech or others will require that you either fabricate your own pellet, or use a hopped-up e-match to light the motor. For my 2nd stage motor I used EX motors, so I was able to use a freshly cored motor lit by an e-match and a Pyrodex pellet jammed in the upper grain. This led to an almost instant-on ignition of the relatively small 29-2G EX motor.
I urge you to give a smaller 2-stager a try, maybe 29mm-29mm, 38mm-38mm, or 54mm-38mm. This will get you familiar with your electronics of choice and confirm that you're able to execute your desired flight profile before going for the bigger attempts.