At the moment, probably by cheating

Eminently possible. Begin by releasing Ma Clique right away as a neutral state, freeing up a whole load of your troops. Rush towards the Yangtze where possible but overall focus on holding the line in mountainous/river terrain. Disband the militias right away as the rest of the units will make better use of their inf equipment

Hold out against their initial onslaught, isolate their spearheads when they rush south (Their better units may even reach Nanning, but that just makes them easier to cut off) And carefully build up a navy. Three things will turn the tide
1-AI overreaction to a breakthrough enabling you to take advantageous terrain elsewhere
2-US Tech which allows you to get some beefy armoured divs to counter the 8+ Chicom tank divs
3-Your navy, and a naval assault by cavalry to rush Beijing-Tianjin-Mukden, with the initial units distracting the garrisons, getting them to pull out of the VP's and then seize them at the same time

Thats' how I won for the first time as NAT China, oh and spend initial political power on new generals as you can get a decent Inf gen especially in the central sector.

Defense of Shanghai, pursue the US equipment focuses and hold the line. PRC will run out of guns eventually, and you have a factory advantage.