Well, in our games, the US player usually doesn’t go 100% Pacific. Usually, a lot depends on whether Germany accomplishes Sealion. If they do, then the US player will usually spend more in the Atlantic to try and liberate the Brits, keep Italy in check and try and get some pressure off of Russia. If Germany doesn’t take London and starts off Barbarossa, then the US player will not spend much in the Atlantic because Britain should be able to harrass Germany enough to help out Russia some. In that case, the US will spend closer to 80% or so in the Pacific and really give Japan a hard time.
I would say the most important thing to do with Japan is get the DEI and keep them, which will probably necessitate destroying the Indian fleet and maybe even ANZAC’s small navy as well. The Philippines, Malaya and Hong Kong are also important grabs. With the DEI (+15), those three territories (+8) and the NO for the DEI (+5), you more than double Japan’s starting income. Grab up as much of China as you can while working your way toward India. Once you have Calcutta in your pocket, Japan should be making plenty of money for more warships and air force to take on the ever growing US Navy.
I wouldn’t mess with trying to take Australia until AFTER you have Calcutta, and even then if you happen to have the chance to do so. Your main priority by this point will be fending off the US Navy and protecting your capital from invasion. Any major push toward Australia could leave you too weak back home and America could swoop in if you are not careful. ANZAC is more of a nuisance than a real threat and if you can manage to keep enough troops on and warships around the DEI, you should be able to more or less neutralize them and deal with USA.
Also, when I play Japan, I almost never attack Russia unless the Pacific war is going really good or Russia moves all those men west. With those 18 infantry, there is too much commitment for too little gain up there.