It is compulsory to have a TFN to work in Australia.
It is a unique number that will identify you as a worker. Every employer will ask you for your TFN. If you still don’t have your TFN after 28 days of working, the taxation rate will raise to 47% of your salary.
Your Tax File Number will be given to you by simple demand on the ATO website. As for the Visa, the sooner you get one, the better !