When playing a 5 player game the major weakness of the allies, lack of co-ordination, becomes a major concern. The axis players can pretty much pursue their own short-term goals. The allies on the other hand aren’t strong enough to mount an effective campaign without the support of the other allied players. I suggest FDR, Churchill, & Stalin meet in Tehran to map out their strategy. :-P
But to answer your question there are a number of strategies for a pacific campaign. When I go for a pacific strategy I try to do 2 things, 1. Split the Japanese fleet & 2. Get them to attack me. You will need some help from the UK.
Combine the UK Indian & Aussie fleets in SZ30 (1fgt, 1ac, 1dd, 1sub, 2trn) japan can attack with 2fgt 1ac 1bb. Japan will most likely win the battle but will lose part of their fleet.
If Japan attacks Pearl Harbor with capital ships (ac bb) counter-attack with your bb, trn, fgt (from W. US), fgt from Hawaii & bomber from E. US. You will most likely lose all of these but if you can deal a serious blow to half the Japanese fleet.
On US1 build at least an AC & transport plus other Naval/Air units, move the dd from sz20 to the US west coast.
After the 3 battles in Round 1 Japan’s fleet should be much dimished & you have a new US fleet to start threatening japan’s IPC lifeline in the South pacific.