Well, You idea on Chinese communists is quite good, and if combined with the following, it would be excellent: I think that for Chinese communist, there should also be one regular army and one corp, one is the 18th army, and one is the New 4th corp. These two armies are regular army in the order of the Nationalist China land forces.
They should be put into bmp file, I’ll help you later.
Well, warlords in China at that time are not so strong as in the 1920’s and 1930’s, in fact except for XinJiang (Sinkiang as you mentioned, however, nowadays, these kinds of spelling of Chinese name are not used, and most Chinese don’t know where or who they are ), which is under rule of warlord Shicai Sheng. For Xianxi (I think this should be spelled as ShanXi better) only the north part is under the control of communists. For Ghuanxi (which should be spelled as Guang Xi), Si Chuan, Qing Hai, the former warlords had already swore obedience to the central government. Menchoekwo ( Which should be spelled as Zhedong Mao) and other communist army also recognized the central government. So I think no need to simulate the warlords.
What’s more, during the war against Japan, the former warlords and their army are under the unified command of the nationalist government, e.g. the GuangXi warlord Chongxi Bai and Zongren Li, and the Si Chuan warlord Xiang Liu.