it's absolutely true that the Dutch (and the Flemish, the people in Belgium who speak a slightly different variant of Dutch) are proud of their foreign language skills, and as a result, sometimes frustrating for foreign learners of Dutch. I just spent my holiday in Spain, and the difference was immense: in Spain, people will address you in Spanish first, even when they can speak good English themselves and can see that you're a tourist who may or may not understand Spanish. If it turns out you don't speak Spanish, then and only then will they switch to English. In Flanders or the Netherlands, most people, especially those who encounter a lot of tourists, would automatically start in English in such a situation (or French, or German, or any other language they may speak if they suspect that's the other person's language).
So if you do this, you will have to be very stubborn about wanting to speak Dutch. With people you only exchange a few sentences with, it's likely to be a lost cause, but you'll have to insist that your friends and closer acquaintances speak Dutch to you and let you speak Dutch to them. I think in any case you should begin your stay with a crash course and keep following classes during that year, but of course not everyone learns a language the same way - some people have more benefit from grammar lessons and formal classes in addition to immersion than others.
As to whether you'll become fluent, it obviously depends on how good you are at languages, how much chances of practicing you get, and many other things. But I would say unless you're very gifted at languages or unless things go badly, you're likely to end up after a year with the ability to have relatively fluent conversations (albeit with a significant and noticeable accent) about not too difficult topics and understand at least the gist of most written texts, more if it's an easy text or on a familiar topic. From that kind of level, you can reach still higher levels through the resources available in Australia or through the internet, I would say.
I'd advise you to make a conscious and informed choice of which language you're going to study, though. Since most people who speak Dutch can make themselves understood (in many cases much more) in English, and since there aren't that many of them anyway - at least when compared to French, Spanish or German - the practical use of Dutch will be limited. It sounds like that's not really your main goal anyway, so Dutch may well be the best choice after all - we'd certainly like to think so - but it's important to deliberate carefully if you're going to put that much effort into this new language.