Why invading Australia would overwhelm Japanese logistics

How fierce would resistance have been to a Japanese attempt to seize a major Australian port in World War II?

Very fierce and logistically punishing: a captured port would still leave immense distances, strong defenses, and a continental campaign to sustain.

Australia's scale separates Perth, Darwin, and Sydney by operationally punishing distances, so an invader would need large forces and sustained armored mobility. Local defenses, terrain, and the difficulty of supporting reconnaissance and landing forces compound the problem.