A few thoughts as Allies...
NO piece of land is important. If the Japs want it let them have it. Delay the if you can, but don't loose forces you don't need to.
Maintaining the integrity of your ground forces IS important. That means don't stick out even Divs on an island. The MINIMUM is about 400 AV and level 4 forts... if you can't do that, don't until you are ready! Put a couple of engineer units and build the forts. Once ready move in the 1-2 Div into their new home.
Train your aircraft hard from day one. DON'T commit them until they are 60-70 in their skill (A-A for fighters). Again you need mass. One base with 50 is MUCH better than 2 with 25.
The aim is to delay as much as possible. Strike where they ain't... but if you don't know where they are don't go there.
Places that are nice to hold are Darwin PM and Fiji/Noumea... but NOT essential to hold. Don't reinforce them until to can generate enough mass.
I agree on Brisbane. I also send forces to Darwin and Alice springs. If you hold Brisbane and Alice you are good.
Perth is tricky. Easy for the Japanese to take unless you reinforce... but you don't have much... Makes a long logistic tail for them... and cuts off supplies and fuel (or you transit to Melbourne). In the end again DON"T LOOSE units trying to hold somthing that you can't have 400 AV and level 4 forts.
Send as much supply and fuel from The middle east to Australia as soon as you can. India (except for Burma) doen't need it, so get it moving NOW.
Use small frces to cause delay, then concentrate the rest into a couple of key well defended locations.
Let them over extend, then go around them later. BUT you can only do this if you haven't lost your infantry formations.
I ship everything I can from the US to PH. Serves two purposes, defends the island, and it is 5 days sailing closer to where you eventually want to go. When in doubt ship to PH is my motto
Any "spare" ships should be moving supply and fuel to PH. Escort the troop and fue carrying convoys, the supply convoys don't unless you have a spare escort... loosing ships and supply isn't important, troops and fuel is important.
Send you convoys DEEP, yes it adds time, but it is SAFE. Having the stuff arrive is better than loosing it to a CV raid or to subs.
Keeping your fleet out of sight will slow him down... in partcular if you get a couple of minor but safe victories (which indicates you could pop up and will use your assets). Just hiding is sort of OK, but you need to demonstrate you will come out to play, if you can get an advantage.
Finally on aircraft your replacements are so low do not use them unless you can generate mass (40-60) or it is very safe.
Good luck!
Rob