I don't want to seem stupid

but are you intending to do
all those things in one weekend?
Unless it's a
really long weekend, I would suggest that popping over to Kangaroo Island isn't worth the time (and sea-sickness!) unless it's for a few days at least as there is heaps to see. Plus it might still be a bit chilly in September.
Perhaps you could to take in the Barrossa, then Lobethal and that area, then down to Victor, Middleton (you never know there might be a stray whale left there!), Granite etc to see the penguins.
Whatever you do, please don't forget to check out our pink-speedo, silver-jacketed indigenous friend....he's famous you know!
Whatever you do, I'm sure you'll have a great time here. There's plenty to do and see.
Have fun!

LC