Hi,
You will be unable to pay class 2 UK National Insurance based on your foreign income as it is not employment.
In relation to the years while you were overseas, the CF83 application form will be issued once it has been assessed. Our current timescales can be viewed here:
Check when you can expect a reply from HMRC
There is no reciprocal agreement between the UK and Australia for social security, only for health care.
The Department for Work and Pensions can assist you with any benefit related queries and the options available to you based on your circumstances.
Contact Jobcentre Plus
Thank you.