Interesting does immigration an issue in this federation? Since sumatra like you mention is having a bad time
Btw does bali ever has any attempt to join this federation? Since if going by the USI state map then bali should be grouped with sulawesi (though i suggest giving it to java since it is much closer and probably has a lot of economic ties)
And i would guess aceh dominated the politics and sharia law is prevelant and the oil fields are one of their source of revenue
For the most part Pasundan doesn't mind receiving cheap Sumatran labour and Sumatra is greatly helped by their remittances but migrants are often used as a bargaining chip in disagreements between the two countries.
Sumatra isn't quite a petrostate but oil is very important to the economy, yes, not just as a source of revenue but also as a way of creating a nexus of corruption and relationships which bind the ruling class together. Its legal system is Sharia but with influences of the colonial Dutch civil code.
What Chen Yi helped Heydrich and his friends? The PRC general or the KMT general?
The PRC general. TTL the survival of the reformed Chinese imperial state means he enters the mainstream military instead of turning to communism.
What exactly lead to China getting involved? Just desire for influence?
Basically that's it. Within China, there's still a lot of turmoil under the surface following the death of the Guangxu Emperor, with different factions battling for influence. So if you're a member of the militarist clique, a quick little victory in Africa is useful boost for your side.