Sydney in September
The weather was not so nice: windy, rainy and pretty cold (from 10° to 20°) but when the sun went out it was a completely different story. You can move around in the city center on foot, it's not too big, while if you want to go further no problem: the public transports are very efficient. I won't describe here what you can find on a guide book but I can tell you that 5 day are enough to see what Sydney offers without rush.
Insider Tip:If you are going to take public transports (train, bus, ferry) you should better get the Opal card. It is a rechargeable card available almost everywhere.