Did the Japanese plan to invade Australia or were they not able to because of limited resources?
The Japanese certainly had an interest in doing so. The most famous is an instance of 3 tiny Japanese submarines attacking Sydney Harbor, 2 of which were destroyed. Source 5t
There are also many other tales, a couple of which have been verified to the true. Source 2b However it's hard to tell which is real and which is fake without official support and every year more and more veterans die without their stories being recorded by historians.
One such story is an older gentleman I met on the train wearing the WW2 service ribbon and I believe (Though my memory may be hazy) a green, yellow, red ribbon - possibly the Pacific Star ribbon. He claimed that he was repelling a Japanese landing in Western Australia as a rifleman in an APC with a narrow slit in it - possibly a Kangaroo. If I'd known the significance of this event I would've asked the man's name, but I was too young to know.
International Level: Politics 101 / Political Participation: 1 0.1%