I partly disagree that rejected offers are always useful pricing data. They tell you what did not secure that particular property, but not necessarily its final price or whether the seller chose another offer for cleaner terms or timing. Still, they can improve your process. While the details...
ZAR 8,600,000, based on the asking price and the unusually large 165 m² floor area. That said, the missing fact is local supply: if several similar 3-beds are available, the size alone may not protect the price.
You have checked the deposit and estimated closing costs; the unclear part is what becomes payable immediately after completion. I would protect the normal emergency reserve first, then account separately for moving, the insurance excess, the next mortgage instalment and any building charges due...