The ATO does not require Strata Plans to pay tax provided they're covered by the principle of mutuality, that is, the Plan's only income is derived from the Levy Contributions paid by its Proprietors.
Sadly, most Plans receive interest on their funds, the Sinking Fund in particular, and so should pay Company Tax on that and any other income.
So far as the GST is concerned, if the value of your Plan's taxable supplies exceeds the threshold and its GST Registered, shouldn't it be calculating its annual budgets with all amounts as GST inclusive only where that applies?
That is, in the case of water usage the amount shown in the Administrative Fund budget does not include GST, and in the case of contracted services such as grounds maintenance the amount shown includes GST, and when all budget items are summed, the total is GST inclusive (but only where applicable).
Levy Contributions are then shown as GST Inclusive on Tax Invoices.
I hope that's the correct approach, because that's what I'm doing; but then our Plan's not GST Registered as our taxable supplies (Levies) don't exceed the threshold simply because self-management keeps our costs down.