Planning of warheads numbers need to make some really conservative assumptions on adversary BMD, failure rate, first strike losses and so on.
Even 100 MT sized warheads landing around the US is enough to end the country. Imagine your top 100 cities and urban areas gone, fallout everywhere, no healthcare, no emergency services, no work jobs productivity for foreseeable future. No safe food if you can find food, no water at all unless it is imported so coastal regions or border regions might fare better. Now double that and double it two more times and you approach 1000 warheads. Obviously this is planned out with some proper methods but I doubt more than 1000 warheads reserved just for the US is too few. I doubt China is aiming to go nuts with this stuff like the US and Russia have and build >3000 warheads.
Russian warheads have to cover North American, Europe, and China. US warheads just Russia and China. Chinese warheads must be numerous enough to cover US, Europe, and some parts of Russia (last priority for build up). Overall if 1000 reserved just for US, the total number would start approaching 2000 if we account for Europe, Australia, India. None of them have BMD in the league of US, China, and Russia. Japan is relatively small in size.
So long term goal would be similar size to US stockpile but depends on how necessary it is to keep reserves for Russia.
Stockpile should reflect US potentially performing first strike. China needs to improve delivery and early warning with several layers of redundancy. Numbers are being corrected and so is delivery with new 096 being constructed, DF-41, JL-3, upgraded DF-5 and HGVs. Since older generation of Chinese early warning is long phased out, there is no known new land based early warning of considerable size. Just mobile radar units of much smaller capacities and Type 346 variants at sea. That's not enough since it doesn't cover the northern approach through Russia.
There might be some space based early warning since China's been launching dozens of secretive military satellites for decades now. Still would like to see some giant mountain face phased arrays like China had in the past.