I'm playing HOI4 again and my god it's engrossing. I've tried two different scenarios in the last couple of weeks: trying to go for a Communist South Africa and leading an anti-colonial crusade in Africa (which I aborted for now because it seems extremely difficult) and leading Mao's Chinese Communist Party to world conquest by, maybe, 1960? Not sure how plausible it will be to do that.
Playing Communist China with the standard historical AI settings on is very difficult. I believe that every single HOI4 game I've ever played (though admittedly before I started playing again last week I had only played Nazi Germany and the Soviet Union) saw Japan completely overrun China. With Communist China you have access to essentially zero heavy weapons for most of the game, you're stuck building small arms and recruiting infantry divisions. So resisting the Japanese is quite difficult. One of their divisions can push back three or four of yours, easily, unless you're sitting in mountains or across a river.
Anyway, I settled on some settings for the game that I think make world-conquest as the Chinese Communists a bit more plausible and fun. First I set the Germans to Kaiserreich, which makes the German AI revolt against Hitler, installing military rule before bringing back the Kaiser. I set the Japanese to Neutral, which makes them strike at the Soviet Union rather than invading China. And just for giggles I set Australia and South Africa to go Communist. I'm thinking they will eventually make helpful allies/puppets.
I can't remember whether I set the Soviet Union to attack the capitalist powers in the Middle East first rather than establishing a buffer in eastern Europe. Either way it won't matter much; Germany hopefully won't be going all-out in Barbarossa so the idea is that the main action will be Japan vs USSR (hopefully Germany can attack the western Allies and bog them down some while I make moves to grab some oil and whatnot e.g. from French Indochina).
Anyway, playing my first runthrough with these settings I conquered Shaanxi, Xibei San Ma, Sinkiang, and Tibet before I had to go to bed, with my armies lined up on the border with Republican China. I'm not 100% sure where to go from here but I've equipped my divisions with supporting artillery and some other support companies and started recruiting cavalry units, so I'm feeling pretty good about the course of the game. I'll probably take some of the national focuses that relate to the Chinese Civil war in preparation for attempting to take over the rest of China, but my next actions will probably be dictated by what happens between Japan and the USSR and how soon.