Cascade. They are the most fruitful of all, easiest to grow, and everybody knows and loves them.
Citra. The new Cascade of the 21st century that most everybody knows and loves. Or alternatively, down under by you, maybe you'd prefer Galaxy which is very similar.
Hallertau. The classic that everybody knows and loves. Not quite as fruitful, but not bad, and you'll never have a problem selling them.
Magnum. High alpha Hallertau. Used for bittering by everyone everywhere.
And that's about it. Those are the essentials IMO. You can make pretty much any beer style with one or more of these versatile hops, never have a problem selling them. They're not just fads. They'll keep you profitable for generations to come, guaranteed.