I've never defended Oz, but I'd say stay off the water with troops. The railroads are your friend. That said, I'd hold Perth if at all possible and not move those troops away. There's nothing in the NW worth risking Perth's advantages.
Be aware of where the Line of Death runs and the reenforcement package if he crosses it. Get some ships to the entry locations to lift those troops somewhere.
If he's willing to activate the package there are invasion routes into west Australia from the south which could surprise you as well as cut Perth off from the rail network. Don't let him get to Kalgoorie.
I'd take a good look at the Japanese garrison requirements for the eastern coast cities. Oz can soak up some serious garrisoning.
Why are you bothering to use B-17s on PM if it's gone? Guard those puppies someplace safe and deep. You may need them to bomb troops on road march. PM just wears them out.
Line of death? Time to crack open my manual again I see.
Im striking PM mostly to force him to put fighters there. Attrit Attrit. In my many games as Japan my opponents just attrited me to death where ever I had forces in range of their heavies. Currently PM is the only place I "can" strike him with them. (Burma could be hit as well, but so far I am keeping that mostly Royal Air Force).
Probably wise regarding Perth. I don't see him driving that deep (or far to the west) into Australia has he has been content to sit at Daly Waters.
Much like China where after just kicking my ass across Asia, he has just sat at Sian...boggles my mind but it has given me time to get troops into position to defend the core area of that country.
Take a look at this thread
there's a screen shot for each unit in the package. They come in at CT and Aden from memory, but I'd check that in the editor.
The LOD is south of Brisbane I think (been a long time since I looked), and it's on a strict x,y basis. Since Oz is very sway-backed in the game due to map projection, you have to be very careful to use the y-coordinate to see where it is out west.
On the B-17s, it's your call, but he can make more fighters; you can't make more B-17s. You won't attrit him out of fighters. But B-17s are your best 4E ground attack bomber until the B-29. Oz has a lot of open, desert terrain which bombs real good.
And if he wants Perth he won't walk there. He'll come by sea.