Compliance is the part of event planning nobody posts about, and the part that shuts a gate on the night when it is missed. Requirements vary by local government area and by venue, so treat this as the map, not the territory.
Start with the venue
Established venues often hold standing approvals that cover an event held on their premises. Ask directly what their licence covers and what it leaves to you, in writing. An outdoor or unconventional space almost always leaves everything to you.
Local government clearance
Public gatherings usually require notification or a permit from the LGA where the event is held. Fees and processing times vary. Two to four weeks is a sensible allowance.
Police and crowd control
For a sizeable crowd, notify the divisional police station covering the venue and agree the security arrangement. This is both a legal expectation and practical protection.
Music licensing
Playing recorded or performed music publicly can carry a licensing obligation to the relevant collecting society. It is inexpensive relative to the event and awkward to resolve retrospectively.
Fire safety and medical
Know your exits, keep them clear, and have a first aid presence proportionate to headcount. For large crowds, an ambulance on standby is not an extravagance.
Keep the paperwork on you
Physical copies, on the night, in the hands of whoever is at the gate. The approval that is sitting in an inbox is the same as no approval at all when someone official is standing in front of you.