Material lead times and permit timing need their own sequence, not just notes in the budget. Ask contractors which selections must be locked before demolition, what can be substituted without redesign, and which activities depend on approvals. I would also identify a minimum viable finish...
Is A$3,512 a verified long-term monthly rent, or an estimate based on short stays or peak-season advertising? That is roughly A$42,144 a year, so the 8.5% calculation works, but the unusually strong yield makes the rent assumption the part I would challenge first. Ask for comparable settled...