Steps

Pick the window
Default to March, April, May, September & October; write a reason if you choose January.
Read the yellow months on the heatmap first.
Check entry
Electronic travel authorisation is typical; apply before flying.
Check the six-month passport rule in the same sitting.
Pick regions
Two of Sydney, Melbourne, Great Barrier Reef is enough.
A transfer day is not a sightseeing day.
Lock stays
Lock a Sydney harbour style stay before peak.
For honeymoons, room position beats star count.
Shape transport
Use Sydney-Blue Mountains-Canberra as the spine; cut side quests.
Put the last night near the airport.
Leave slack
Leave a weather/strike/tender day empty.
An empty afternoon is the actual honeymoon luxury.

Entry

Passport — Electronic travel authorisation is typical; apply before flying.
Insurance — Match travel insurance to the dates, including medical evacuation.
Connections — Do not cut LHR / JFK / LAX connections against a night arrival.
Local rules — Drone, temple dress and smoking rules fine faster than a tip.

layers — Pack for Australia diurnal swing and indoor heating/cooling together.
rain shell — Pack for Australia diurnal swing and indoor heating/cooling together.
walking shoes — Pack for Australia diurnal swing and indoor heating/cooling together.
adapter — Pack for Australia diurnal swing and indoor heating/cooling together.
copies — Pack for Australia diurnal swing and indoor heating/cooling together.

Peak as default — Do not pick January just because the month is famous.
Three cities a day — When transfers become the plot, places become a backdrop.
Fake fares — Numbers here are bands, not today’s search-box fare.
Ignoring jet lag — Do not put a dawn shoot the morning after a 15h flight.

Craft does not kill romance. It kills queues.