You have so many options with Japan, because you have up to 5 nations to contest with (If/when you go to war with Russia).
I prefer handling China first, which means ferrying in units to Kwangsi early on so that you can continue to deny China the Burma Road. I’ve yet to build an IC on the mainland, but I hear that helps.
The longer you wait to take the Philippines and DEI, the worse off your situation becomes. Each round India and Anzac are collecting IPC, the worse the economic disparity becomes for Japan. Taking and holding those locations make it increasingly difficult for the allies to reclaim them from Japanese hands (Generally the US has to get deep into the south pacific for that to change). In one fell swoop you can make more IPC by going to war, than relying on the 10 IPC for being neutral - WHILE cutting off their IPC income. Usually J2 seems to make sense to start the South Pacific Island war, so that you minimize the IPC gains of India and Anzac.
You don’t want the UK stack of Infantry sitting in Yunnan, because you’ll be hard pressed to reclaim it once that happen(Read lose lots of Fighters to retake it). That is why the threat on India becomes so important and why Kill India First helps two fold: Kills off China and keeps the Burma road cut off. Last thing you want is Chinese Infantry backed by artillery reclaiming all those IPC’s you gained in China on J1-J3.
The only real issue is dealing with the US advancing on Japan - so don’t forget to keep a solid garrison on Tokyo. Allow the US to sit in SZ6, you can lose up to 11 IPC. Sometimes placing DD blockers between Hawaii and SZ6 can buy you one less round of Convoy. 8 IPC to prevent losing 3 IPC is the net-net effect.
However, the US will never get enough units there to take it if you head for Hawaii and cut off their transport supply lines while you up your stack of units in Japan. Besides, you’ll make enough IPC from taking India to weather a round or two of Convoy until the US realizes its aggressive move into SZ6 left them as sitting ducks until your aircraft from India get in range of SZ6 and its supply lines are cut off.
This is why it sometimes makes sense to put the IC Kwangsi and a NB on Hainan. You can put some extra fleet units at a minor there, and they are in range to hit SZ6, but the US fleet can’t reach them in one turn. That NB in Hainan also allows you to get back to SZ6 from India in 2 rounds instead of 3 as well as to get to the Caroline Islands in 2 rounds instead of 3 if you decide to ignore the US convoy raiding in SZ6 and head straight for Anzac.