This is the basic J1 attack:
Take PI with 2 transports (2 inf 1 art 1 tank) from home fleet + cv from Truk (planes in land battle) + okinawa fleet.
Eliminate UK BB (and transports) with 3 Bmb + Formosa fighter. (wonder if you knew about this move)
Kill New Britain sub with DD
Kill Hawaii Tr with SS
Take Kwantung, Yunan, etc… with troops and planes on continent + additional planes from Japan.
Speed is critical for Japan. You have to neutralize UK/China in 3-4 turns. If you find yourself having to spend heavily on mainland forces as well as building your navy the allies have won.