I usually do it that way:
economic part
1. research priorities: inf, cav, mar, mo, art, ground doc + tac tech /docs
2. upgrade the old divisions
3. build first mountaineers + art brig (12-18) and group them in stacks of 3
4. as soons as marines are available (normally ~mid'37) build 12-18 divs+art in stacks of three
5. build some inf in times of surplus ics + maybe 1-3 hqs
6. research carrier tec in '37
military part
1. group all available land units you start with in manchuko in stacks of 6
2. after marco polo rush down south through shanxi. the line changzi-quindao should be reached easily
3. one beach landing shanghai or nantong with mountaineers and strike for nanjing, 6-9 divs should be sufficient, you can also use the gar divs to garrison your beaches while the regulars move inland
4. nat china will move the bulk of their troops up north to face your manchuko armies -> make a landing in fuzhou or xiamen with mountaineers (a 3 div stack should be sufficient). if this is not working try to expand your nanjing beachhead further south
5. soon the front line will be from the borders of com china in the east to the east china sea in the west and down south to bao'an. at this point most of the units you built as written in the economic part should be ready for duty
6. use the new-built mo/mar to conquer south nat china / guanxi clique. the nat china troops concentrated in the east/north will now fall back to defend their threatened capital so you can easily advance through china
7. attack always from different provinces, use the advantages of mountaineers (speed+attack/defence) in south china to create pockets
8. build + use 2 full stacks of tac bombers to hammer down the org of nat chinas divs
9. don't go for kills - you have the advantage of much higher organization than nat china, so you don't have to rest after taking a new province. push your troops foward as soon as possible, use the bombers to kill retreating troops
with this strategy you should celebrate victory in '38-'39, which spares two more years in gearing up for the US. The nice one: You got already enough special divisions (mo/mar) and a core carrier task force for war in east india / pacifica and later at the us beachheads and can now concentrate on air tech / equipment and building some mech/mot/arm armies... and the one or another nuclear reactor
