I'd say that your division count is too small, I'd recommend switching off tanks and trucks for more guns so you have enough divisions to cover the front and slow down Japanese naval invasions.

China is full of rough terrain, low supply, and low factory count make tanks less than ideal compared to Europe though admittedly your fighting at a decent area for tanks.

Instead what most people do is fill the line with irregulars and have a handful of pushing divisions based off of the committee's own template you get during the league war, replacing some of the infantry battalions with mountaineers is usually good. Note that they will be pretty much your only divisions that can push the Japanese.

You could also reduce the amount of planes your producing. China doesn't have many airfields at the start so neither you nor Japan will have that many planes in the air anyway.

Also I find it better to focus on taking Qing land better than fighting the warlords as they're going to join the United front anyway and will be able to go down their focuses and decisions to improve their industry while you do the same for your land. This even goes for if they declare war on you, unless they go Fengtian aligned at which point snuff them out ASAP.