I think a -50 TUV swing is probably acceptable losses for Japan. You loot about 10 IPCs if you sack India on turn 3, and you collect 3 IPCs for the territory plus 5 IPCs for the NO each turn, and you also deny the Allies about 6 IPCs per turn in ongoing income. Sure, you can lower UK Pacific income below 6 IPCs with subs, bombing, etc., but actually conquering India frees up those subs and bombers for other campaigns, so I think it’s still fair to count the UK Pacific income at 6 IPCs.
So you’re looking at a 10 + 8 + 6 = 24 IPC swing on turn 3, followed by an 8 + 6 = 14 IPC swing on turn 4, and another 14 IPCs on turn 5, meaning you’ve essentially broken even by turn 5. It’s not literally the best economic investment Japan could make, but it gets you a victory city and denies the Allies a lot of strategic options and puts pressure on the Middle East / Stalingrad region and consolidates your rear so you can focus on confronting USA / ANZAC without any naval threats to your west. It’s a good deal for Japan if you can get India for only 50 IPCs of net TUV loss.
I think a -90 TUV swing is probably cost prohibitive – at that point you’re likely to have so few planes left that America can get the jump on you, force you out of the Philippines and the money islands, and send you into a death spiral. Theoretically you would eventually pay off your investment if you continue to hold India, but in practice you will lose so much ground to America that the net swing will be in America’s favor, not in your favor. E.g. if America takes just Borneo and the Philippines from you, that’s a swing of 4 + 4 + 2 + 5 = 15 IPCs (or more if that costs you the money island NO), so you’re already net negative trading Borneo + Philippines for India. If you can take and hold West India and Shan State too that makes it 15 IPCs vs. 17 IPCs, so technically you’re up 2 IPCs…but it will take you forever to pay off a 90 IPC investment at 2 IPCs per turn. That’s not a good deal.
I’m unclear on how/why you lose 3 infantry attacking Java – what’s on Java besides 3 ANZAC fighters? Are you assuming all 3 of the fighters score a hit?