On a permanent level, Australia has a permanent program of around 180,000 places a year in a country with only 22 million people.
But I don't understand why you'd want to leave, having lived in the US, UK, Australia, South Africa and NZ, the choice of NZ for ease of doing business and life is easy.
However, one big deterrent is proximity to the rest of the world. If you want to travel home to visit family, or due to an emergency - it's going to cost a lot of money and time.
Because of the distance, the logistics of physically moving there are also that much more difficult.
Then there are the mainstays - cost of living in/around major cities is quite high (though in the ICT sector earning potential is quite good), there are lots of scary critters, etc.
Many plumbers are also qualified in drainlaying, gasfitting and roofing as well. If you work with gas then lives depend on the quality of your work.
You also have to be physically fit, willing to get up early and sometimes deal with really unpleasant situations (e.g. wade through shit).
"Average" plumbers in AU might only get 60-80k (seriously, check the ads), which is actually not that great an ROI on the investment.
It's not until you specialise, become senior, go out on your own or start doing lots of overtime that you make money.
On Bloomberg I listened to an interview with the founder of Jetstar airlines, currently owned by Qantas, and who is now expanding a renewables business, who called Australia a resource exchange economy. Reading how cooks can earn $325K a year in gas projects, and noticing that the just signed Australia - Japan free trade agreement is mostly beef and agriproducts in exchange for TV's and other electronics, the sense initially is of lack of diversity in tech.
There's no way I could make my hardware project in Australia, not that I ever intended to. I haven't been able to find a single viable option for PCB manufacture. And if a company can provide them they're almost always farmed out to China in any case.
In the UK and the US, but also Europe it's just much richer in scope and size. There are some outstanding hardware facilities in the US. They're virtually non existent in Australia, at the right level of expertise and scale.