A good question.
A local answer.

Reserve several nights for Perth and Fremantle, then build a slower southwest loop around two or three bases. Account for the return to Perth before adding a distant coast section.

Choose a realistic turnaround point instead of trying to reach every landmark in one short trip. Carry water, food and a fuel plan between towns.

Keep Rottnest as a Perth-based day and check ferry times before fixing the final nights. It does not need a separate accommodation move.

Give Rottnest its own day and check ferry timing, stroller rules and weather before committing. A toddler's nap schedule may be easier with fewer fixed bookings.

Book flexible outdoor plans and pack layers for coast and inland differences. A vineyard or walking day is easier to move than a fixed transport booking.

Ask hotels about a guaranteed late checkout or day-use room before booking; a casual request on departure day may be declined. Confirm when pool access ends.

Visit earlier on hot holiday days and pack shade and water. Avoid promising a safe swimming spot based on a beach's usual reputation; conditions change daily.

Treat wildlife sightings as a bonus, not a guaranteed beach activity. Check the season and weather for boat tours, and leave time for safe coastal walking.

Choose accommodation near the streets you expect to use after dinner and check parking if you will have a car. The port and beach areas feel different at night.

Compare the total ten-night cost of room and parking, not just the advertised nightly rate. A slightly farther apartment with included parking may cost less overall.

Use official road-condition updates before departure and avoid driving at dusk or after dark when wildlife risk rises. Carry water and an offline map.

Allow extra range for regional driving and have a backup charging stop. Compare the total rental and charging convenience with a petrol car for your actual route.