Hi,
I went backpacking in 2006 for 7 months on my own around Australia. I booked my WHV, flights and first backpackers through STA. You don't want to book any longer than one week in your first hostel as hostels vary in their characteristics wisely. use word of mouth through other backpackers to find out the best place to stay, or extend your stay at your original backpackers if you like it there.
on your first day or so you can quickly and easily set up a bank account, as you will need to give them an address.
I would always take a backpack rather than a suitcase, it's easier to get around and if you do any backpacker tours space is sometimes fairly restricted to one bag each.
A word of warning though- you will fall in love with Australia, after the most amazing 7 months of my life in 2006, a great return visit 2 years ago, I am now emigrating to Perth next week! Have fun on your adventure!