I just crush the smaller warlord states from Shanxi to Xinjiang, Tibet if there's time, not join with the KMT when Japan declares war and let the two duke it out while both mass training infantry groups for holding the borders while building up industry and properly equipped divisions to punch through whatever forces I'll fight when one side capitulate. I'll even have some motorized and horsey lads on stand-by to rapidly advance the front lines as rapidly as possible should the KMT (majority of the time I've seen them get thrashed by the imperialists) lose and all their divisions get deleted by their capitulation. After that it just turns into a slugging fest of grinding the Japanese imperialists down in equipment and bleeding them white in manpower. If I get enough industry going, I'll go through modernizing the army (converting the all-infantry divisions made to block and hold the front lines into proper divisions with arty and AA brigades, engi, logi, AT, medi, and recon. Motorized if possible), building towards air supremacy, building tactical bombers for CAS and whatever, and lastly building roflstomping medium tanks with mechanized infantry divisions for punching through soft areas to perform encirclement maneuvers. After liberating China I spend time building enough navy to invade Japan with airborne divisions dropped in to support the naval landings, with the time spent waiting for the navy to build bring used productively in bombing Japan's industries, shredding their airforce, and naval bombing their fleets to the bottom of the ocean.

That's my long and slow version though, with a 100% independent Communist China campaign with no cheeses.