Thinking about central and Northern Australia be aware that distances are vast if traveling on land. This makes for a an awe insprising 'feel', but can burn a lot of time and money. I really would not be doing this alone. It's shockingly easy to get stuck 'nowhere' for days on end. eg. a tiny amount of rain 500km away can flood the road your'e on to totally impassable in a few minutes. A lot of 'highways' are'nt sealed.
If you plan ahead reasonably well there are very cheap flights on all the mining routes. eg, Brisbane to Mackay for as little as $59 if you're lucky. Mackay is the gateway to the Whitsundays, nice but touristy. (and, of course, coal central...)
Transport into central Australia is best done on the railway that runs north-south (Adelaide/Darwin/Adelaide). You will get to see vast areas of central Australia, but photo ops will be limited as the train moves constantly.
If you fly into places, (Alic Springs say) you will need some type of transport. The bigger attractions (er, Ayres rock say) will of course have tourist transport, but you will be stuck with the happy snappers, the light will always be wrong/flat/etc.
Organised tours will be safest.
In NZ on the other hand, even in rainy cold august, you can hire a cheap car (say 10 yr old corolla or the like) and tour the whole country on your own. Normal tourist saftey for a 'western' country of course, but stay in country pubs, small town motels etc. I rode motorbike there for years, our strategy was 'if it's raining in the east, go west, raining in the west, go east. Hardly ever more than 1/2 a day coast to coast.

Feel free to ask for more (I can be positive, really<grin>).

MattPC