Condor22 has the idea.
Coming to SA in Winter is not going to be seeing it at its moderate best, but that is with anywhere.
Tourism SA
https://southaustralia.com/
You can call them and ask for suggestions, be aware they might not be that helpful.
Self planning outdoors
https://southaustralia.com/things-to-do/nature-and-outdoor
7 days in Goolwa,
Goolwa is at the Murray Mouth but you need a 4WD to actually get to it, or there are boat cruises that do day trip from Goolwa to the mouth and into the Coorong.
Not too expensive last I looked, and easy way to look at nature.
From Goolwa to Port Elliot, Pt Elliot beach has a lot of Detectorists hunt there, it is a small horse shoe shaped beach, nice spot. Then on to Victor Harbour, "Encounter Bay" Mathew Flinders met a French ship in this Bay, they had a cup of tea instead of shooting each other up (British and French at War at that time).
Granite Island
The Bluff
Whale Centre / watching
Fish Farm just off the coast, you can tour and even swim with them
They have a tourist centre there also
VH to Cape Jervois,
There are a number of tourist walks in National Parks (you pay online for an entry permit)
Good fishing beaches, and for a walk (Kato detected Waitpinga Beach at the Western end by the rocks (a carpark above) found some interesting stuff old and new.
From VH Bluff there is a bushwalk all the way to Cp Jervois along the coast. But no shops or anything.
C Jervios is where you will get onto the Ferry to KI
Nice small beaches around C Jervois
Heading toward Adelaide from C Jerv there are small towns and beaches, wineries etc, day tripping stuff.
Back to the Adelaide Hills from Goolwa, you can get to a lot of Towns and follow the path to Barossa Valley wineries and historic tours.
There are Coach tours for wineries (safe for your license and you can drink without fear.) in the Goolwa region and Adelaide Hills/Barossa
Book with Nenad or at least consult him, you never know how it may work out unless you ask.
Down the South East, it is a bit of a long and colourless trip, but there are some good things to see.
Same heading to the Flinders Ranges, but out North you have towns that are historically detectable and rail towns almost gone now, research that.
KI is a great destination, you should enjoy that place, cant help but to be a tourist on an overseas trip when you are there. LOL
There are some weird and strange tours in Adelaide, some historical, etc Lots of building history, museums etc
Hope I may have helped any..