There's a minimum trade size of A$10 (including FX and any other fees).
There's a maximum trade size of A$10,000.
You also can't have more than A$20,000 in total unsettled buy orders at any one time.
The minimum sale value is A$5. However, there's no minimum sale value if you're selling your total holdings.
The limits for investment plans are the same as for buy orders, however investment plans may be impacted by the 'unsettled buy orders' threshold. You can learn more here.