Port Noarlunga is lovely, I'm sure you'll like it there even if you prefer to go elsewhere for the longer term. I love winter walks along the beach and nature reserve there. Gorgeous sunny days, a bit of a surf on the water and a gentle breeze. Bliss.
We didn't hire a car when we arrived so can't comment. I do recall the company @samandcraig mention as having been discussed a few times on here and people seem to have found them fine :)