A good question.
A local answer.

Choose the rides and one walking area that matter most rather than buying a pass and trying to do every track.

Choose one main walking section and a clear turnaround time before adding extra lookouts. Rail travel uses a substantial part of the day.

Check the current itinerary, lunch arrangements and cancellation policy before booking. A private tour can be tailored but still cannot shorten the distance.

For a park walk, check current track and weather notices, carry water and set a return time before dark.

It can work if you choose a small number of stops and start early. Check the door-to-door drive from your Sydney base.

A day trip can work if you pick one village and a small number of sights. Check train times and the last return connection before leaving Sydney.

A Blue Mountains day is possible, but an overnight allows walks and viewpoints at a slower pace. Check rail or road conditions and the forecast for the days you choose.

Keep closer outings such as a harbour suburb or coastal walk for independent days. Check weather shortly before the mountain trip, since views can change quickly.

Plan the tour for a day with some weather flexibility and keep the following evening light. A very early pickup can make the day feel longer than advertised.

Choose one mountain town and a small cluster of viewpoints or short tracks. The train journey and local transfers take enough time without adding several distant stops.

Look at the park's current animal list, encounter rules and journey time from your hotel. 'Wildlife park' can still involve managed enclosures, so match expectations to the actual experience.

Build in a backup for disrupted service and verify the last convenient return. A day trip works best with one or two nearby villages or lookouts, not a long checklist.