A good question.
A local answer.

Look at the operator's current timetable and fare for your exact travel date and passenger category.

Leave enough time for the meal, transfer and airport check-in; a short map distance is not the full journey.

Choose one main outing if the connections leave little time at either place, and arrange the final return before setting off.

Keep the city days car-free if your activities are walkable, then collect the car when the regional trip begins.

Take a shorter walk if you also want time by the water; the two activities need separate travel and preparation.

Map the road with daylight, meal and rest breaks; a long cross-island transfer leaves less room for sightseeing than the map suggests.

Check ferry, admission and car pickup times before assigning the attractions to specific days.

Photograph the vehicle at collection and keep the branch contact and return instructions available offline.

Keep time for Port Arthur itself rather than adding too many sights on the transfer day.

Leave a full day for the transfer between bases if you want a relaxed stop rather than a rushed drive.

Ask wineries about current bookings and whether they can suggest a local driver or transfer service for the whole outing.

A car offers flexibility, but only if you are comfortable with the roads and the timing after your flight.