I tend to agree with everything you have said, especially about Japan's potential to become a force to reckon with. The U.S. alliance with the Japanese is the best bet to counter China's aggression.
As you implied, China has internal problems that could take down the ruling CCP. Their economy has matured to the point that it is not able to meet the needs and expectations of its people. Don't hear much about the New Silk Road. It is a financial investment that is over ambitious and over extended. In other words, a money sinkhole.