My general Japanese strategy builds 2 transports on J1 (+ a minor IC or submarines depending on my mood) and to stage for a J2 attack. This usually means some fleet in SZ36 and some fleet in SZ33.
On J2:
A. Generally take Borneo and Malaysia (2 of the 3 starting transports should their turn 1 in sz36)
B. Use the transports you bought on J1 to take the Philippines and Hong Kong.
C. Use the third original transport (which in my case is usually in SZ6) for the Philippines as well (to be in position to hit the DEI next turn)
D. Sink any Allied fleets you can hit for a good exchange.
E. Keep hammering China
On J3:
Seize as many Dutch East Indies islands as you can
Keep China in check (if you’re doing well enough, consider annihilating China)
Starting massing men for Calcutta OR push through China to back-stab the USSR
Later turns:
Consider taking Siberia, Sakha, and Soviet Far East (one landing in SIB, then branch out over land)
Maintain a good economy and a good fleet as long as possible. Don’t expect the Allies to let you win in the Pacific, but make sure they have to keep spending there to stop you.
This is a general plan, which you may note doesn’t set a timetable to sack any Allied capitols. I advocate patience with Calcutta, they aren’t going anywhere if you knock them down to 6 IPC. If you want to prioritize Calcutta over the Soviet Union, build a factory in FIC.