If you can't decide which to buy first, a road or Mtn bike, buy the one that you'll use the most at the beginning.
One advantage of road bikes is that you can ride them starting right at your front door, whereas many people need to drive to decent mtn biking areas.
If there are trails nearby that you can ride your mtn bike to, you might start with a Mtn bike, and use combination tires that will be OK on the road so you can ride to the beginning of the off road trails.
Being about as far form Australia as you could possibly get, I can't help you with local choices and prices of bikes, but I do know that there a large communities of both road and Mtn bikers there. I suggest you start with the local shops and scope out your options.
One advantage of road bikes is that you can ride them starting right at your front door, whereas many people need to drive to decent mtn biking areas.
If there are trails nearby that you can ride your mtn bike to, you might start with a Mtn bike, and use combination tires that will be OK on the road so you can ride to the beginning of the off road trails.
Being about as far form Australia as you could possibly get, I can't help you with local choices and prices of bikes, but I do know that there a large communities of both road and Mtn bikers there. I suggest you start with the local shops and scope out your options.