Also, you might run into a problem where the shower arm is too short or angled too sharply for the shower head you bought. This can happen more with the wand-type shower heads and the wall gets in the way of the wand. You can solve this problem by making sure you buy a shower head that fits or installing an extension arm onto the main shower arm. You can find those the same place you buy the shower heads.
Plumbers in Australia have licensing requirements that differ from state to state but it is generally accepted a 4-year apprenticeship with a further minimum experience of 2 years (6 years total) and a further curricular requirement as a benchmark for licensing. Licensed plumbers are also expected to maintain minimum relevant training requirements to maintain their plumbing license