If you are subdividing the subdivision does not give rise to a capital gain and you are ok.
The CGT is paid on the sale of the subdivided block.
Here is the link from the ATO
However, you may make a capital gain or capital loss when you sell the subdivided blocks. The date you acquired the subdivided blocks is the date you acquired the original parcel of land and the cost base of the original land is divided between the subdivided blocks on a reasonable basis.
The 50% discount applies as you have one it for more the 12 months as the purchase date is the initial purchase not the subdivision date.
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