I agree that because it was my first game playing it, that my strategy wasn’t strong. I tried to push too hard with Germany and not establish a strong supply line. Tried to achieve all German Objectives with the first strong push I could make.
With Japan I had all of my transports alive still, and I was building ground units. I decided to push by landing units in North Asia and sweep across the continent, picking up income as I went. I also had bad luck with the Philippines, took me two turns to take that, having to waste units that normally would have been in Asia pushing for the Indian factory. Japan though is pretty sparse for ground units to start out, I didn’t feel that they came on strong until at least turn 3 on the ground at least.
You are right that it would be a better strategy to attack South Asia first and ignore China, but they could become pesky still if you let them linger too long.