A good question.
A local answer.

Use a central base for easy meals and leave a flexible day for weather or a rest. A tram or short bus trip can make Glenelg manageable without renting a car for all six days.

Price the complete rental at the same pickup and return times, including the one-way fee, permitted roads, insurance excess and any extra driver. A low daily rate can hide a large return charge.

If using trains or coaches, check the actual timetable and onward transport to your chosen coastal town. Regional services may not connect neatly on the same day.

Compare small-group tours to the Barossa, McLaren Vale and Adelaide Hills by pickup point, total day length and number of stops. Choose the region that fits your food interests.

With only two nights, avoid changing accommodation. Map each candidate's drive to your arrival route, preferred walks and next destination before booking.

A private car can give flexibility, but ask the driver for a fixed itinerary and pickup point. Do not combine distant highlights simply because they appear close on a regional map.

A beach day at Glenelg or a short Adelaide Hills trip is easier with children than forcing an unavailable island crossing. Check transport and opening days first.

If wine is not a priority, do not spend the day on a rushed multi-cellar tour. A garden, village lunch and viewpoint can make a more relaxed trip.

If you decide to take a car to the island, confirm ferry space and the rental company's island and ferry policy before booking either one. Build in weather and return-travel buffers.

Check current tram and bus works before choosing a hotel solely for one line. A central location with several transport options gives you more flexibility across six days.

If the crop is late, make the drive worthwhile with a nearby village, market or short garden visit. Check the farm's rules on outside food and how it charges for fruit you take home.

Choose the Adelaide Hills if you want a mix of scenery, village streets and food without making the entire day about cellar doors. Hahndorf is an easy focal point; leave room for one other stop instead of an ambitious circuit.