Travel Timelines

Now that I'm into mid May almost, it's time to start putting a plan together for Australia next year, & I'm beginning to find that it's more of a conundrum than I thought. Specifically, about how much time I ultimately end up staying in each place. It's like a work in progess, at the very beginning. If anyone out there has any good travel advice, I absolutely welcome it.I will be going to four different places, Melbourne, Sydney, Newcastle & Brisbane, I've been debating between 2 weeks vs. 10-12 days & lately, I've been starting to think more towards the 10-12 days, rather than 2 whole weeks. What to do, what to do...