The problem of working in Australia.

The answer to your question is as follows:

1. There are restrictions on studying in Australia, generally no more than 20 hours per week, and there are no restrictions on holidays. How much money you can earn depends on the job you find and your ability. I know a student who can earn 2000 Australian dollars a month by working. It's really amazing, but the work is very tiring. If you work in a restaurant like you said, you shouldn't get so much. Generally speaking, an hour is about 10 Australian dollars.

2. How long you study depends on what courses you study. Generally, if you want to immigrate, you have to study for more than two years before you can submit an immigration application to the Immigration Bureau. If you have good language scores and major in immigration, you are likely to get PR.

I hope I can help you and wish you an early realization of your dream.