Self-employed is taken to mean people that work in own their own business (either incorporated or unincorporated). Whether the person has employees or not has no bearing on whether they are defined as self-employed person.
The best source of data on self-employed persons in Australia is the Australian Bureau of Statistics' (ABS) Forms of Employment Survey (catalogue no. 6359.0). FOES contains estimates of the number of owner-managers of incorporated businesses and the number of owner-managers of unincorporated businesses, which together comprise the self-employed.
An alternative method of calculation is to use information from the annual ABS Employee Earnings, Benefits and Trade Union Membership (catalogue no. 6310.0), together with information from the ABS Labour Force, Australia, detailed - electronic delivery, quarterly datacubes (catalogue no. 6291.0.55.003). The employee owner-managers of incorporated enterprises from EEBTUM can be aggregated with the own-account workers (persons employed in their own unincorporated business that don't have employees) and employers (persons employed in their own unincorporated business that do have employees) from 6291.