How many side trips fit into eight days based in Sydney?

If food and wine are the reason for a side trip, consider one night in the Hunter Valley rather than a very long out-and-back day. For nature without a car, give the Blue Mountains their own day by train. Put an easier Sydney day between big outings so the holiday still includes a ferry ride, neighbourhood meals and time to follow a recommendation you hear once you arrive.

I would keep four or five days for Sydney itself, then make one or two side trips. Use one city day for the harbour, one for a ferry and beach, and at least one for neighbourhoods and meals without a fixed timetable. The Blue Mountains are a straightforward rail-based day trip. For a second change of scene, choose either the Southern Highlands or the Central Coast according to your interests and transport; both reward a slower pace more than a rapid checklist.

Keep one flexible day for weather or a place you discover after arriving. If your second trip needs a car or tour, book that first and arrange the easier city days around it. Three distant day trips back to back can consume more of the holiday than the destinations themselves.