Check out the link below for a useful article that lays out in detail how to buy btc if you're in Australia, just don't mind the advice about using a broker, use an exchange and purchase it yourself. The article lists the most popular exchange platforms for Australians as well to help you make a decision. Apart from that you should download a wallet to store you coins once you've purchased them, never keep them on the exchange site. You can research these on the internet or check this forum as many threads have covered wallets
https://www.finder.com.au/how-to-buy-bitcoinsAlso feel free to check out our blog post on exchanges, it's a simple but useful guide for beginners:
http://bit.ly/GuideToExchangesAs far as the hardware wallet, yes it is worth it. Cold storage is the safest method for storing your coins. You could carry it around with you on a keychain if you felt more secure with it that way. Otherwise you could also put it in a safe. Truly there are an endless amount of places you could keep it hidden--it's so small! I'd be easier for you to lose it or forget your back-up info for it than someone breaking in and stealing it.
Cheers!