This is a really interesting an well-thought-out timeline. I remember a British mini-series from back in the day where Gemma Jones played Friederick's wife Victoria Louisa (anybody out there remember what that was called?), and I've always wondered what Germany would have been like had he lived. I especially like how the wars have each come earlier, and how this has led to quite a bit of catch-up in terms of military equipment.
I only have a couple of small quibbles:
1) Islamabad was purpose-built by Pakistan to serve as its capital, and as such didn't exist yet OTL, much less ITTL. Zahir Shah would have set up his gov't-in-exile in either Peshawar or Lahore.
2) What does the cold of the Himilayas have to do with the Japanese drive on Calcutta? For one thing, Calcutta is 150-200km west of the Ganges, where you have the British and Germans making their stand, and secondly, the Ganges delta region of Bengal (OTL Bangladesh) is a tropical, waterlogged plain. Sure, they'd have to get through the mountains of Assam to get to the Ganges, but the main fight isn't in the mountains but in the delta...
Other than that, keep on truckin', dude!! You've created a very unique timeline, and I've quite enjoyed it over the past few days reading through it.