Think about what the Chinese need to achieve MAD on the US.
I would say if they can reliably even get through 12 DF-41s with 10 thermonuclear wearheads each that will be enough.
Once US has lost New York, Los Angeles, Washington, Chicago, Miami etc and some of their major ports and critical infrastructure like the Hoover dam then that it is pretty much it for them.
MAD does not simply mean wiping the other country totally put of existence - it is doing enough damage that they are a non-functional state for decades to come.
What? No that is nowhere near enough. 120 ICBM more like rather than 12.
US has hundreds of ballistic missile interceptors from western to eastern pacific and in Canada for polar routes. It has GBI and THAAD on the land and whatever else they hide.
Nope for China, best MAD would be roughly equal arsenal to US and Russia. It can afford to do it. Both USA and USSR in the Cold War had over 5000 warheads each and China's current population size and economy is greater than both USA and USSR combined during 1970s. This is chump change to create at least another 2000 warheads (more than already in arsenal) and even another 500 ICBM and SLBM. Ask why both USA and Russia refuse to disarm to less than 2000 warheads. Yes they have missiles aimed at everyone and everywhere but China has a higher population than both combined and 10 times greater economy than Russia's.