Everything you ever wanted to know about tax file numbers can be found here
Tax file number essentials (Welcome to the Aussie tax system

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No, you dont NEED a bank account if you are working here but it would make life a whole lot easier if you did have one. Most employers will ask to put your pay into a bank account rather than giving you ca$h. It is relatively easy to open one up (and no, your UK Halifax will not be any use to you, other than to get money out of via an atm) - all you need is 100 point identification (things like birth certificate, passport, photographic drivers licence etc) and they will sign you up straight away.
Not sure about your friend though, other than that she could come on a long term holiday visa but that would not allow her to work.