You're picking a great time of year to visit the Southern Highlands, though the weather can be radically different between early and late fall, depending on where you're at. Mid-September will be very much like summer, with the nights alittle cool but not cold. By the end of october, the nights are getting pretty cold and you can have cold weather during the day as well.
In addition to what you're normally carrying for summer, I would add a full set of long underwear, something around Cap2 weight. I would also add a puffy, either as a supplement or replacement for the fleece. Nice in camp, on rest stops, and to supplement your sleeping system. Down or synthetic is your choice, although if your hiking will mostly be in the Southeast a synthetic might be a more appropriate choice. And raingear; you're less likely to need it in fall than any other time of year, but I would still carry it unless I knew for certain it wouldn't rain. All these worn together while sleeping will boost your sleeping system's warmth quite a bit, though I wouln't wear the raingear in my bag unless it were really cold.
If you're cold natured, plan for hot drinks in camp. A nice heavy meal with lots of fat content will keep the furmace stoked all night. Use a hot water bottle in camp inside your jacket to add warmth, and also to warm up your bag before going to bed. Make sure your sleeping pad is adequate for the expected temps.
Have a great time!