You will generally need to consult an Engineer, this should be done very early on in consultation with your builder and architect, but do not do your final drawings until you have approval.
Councils take a long time to approve works (this varies between councils) so plan accordingly and expect this.
Sydney Water may hold up your approval as well if there are assets belonging to them near your proposed building works. Sydney Water Tap In
You will need to get a Dial before you Dig certificate