They don't want 4 billion Chinese, they have deliberately reduced their population with the one child policy, they want 1 billion Chinese in their country. There is too many of them already. Without the 1 child policy their population would have swelled to 2.5-3 billion and the country would have collapsed under its own weight.
They got rich without taking over foreign lands, or firing a single bullet, why would they change course? They are getting richer and more advanced every year. It's an insular people and culture, not a seafaring colonial empire. If that were the case, they would have long taken Australia, Indonesia, the Philippines and NZ long before the Brits, Dutch and Spaniards got there, the natives of these areas being primitive. The one country they did try to take over and failed several times was Vietnam, who are not that dissimilar from the Cantonese north of the border. The Chinese couldn't fight the locals and the malaria that came with that territory.