How many exactly does China need? The US has 279 C-17s and that's with global commitments in mind. Granted China has a large need for transport aircraft since SCS and far inland bases are more accessible via air transport, but is more than 150-200 really needed?
Yes, absolutely.
In fact, I'd argue for
400-500x Y-20s - And that's just for
transport, tankers and MRTT-type combi variants alone.
Speaking of tankers (including the MRTT-type) - They aren't merely about extending the combat ranges of fighters, bombers and special mission aircrafts (namely AEW&C, ELINT & SIGINT, EW & ECM, MP & ASW, etc) - They are also extremely crucial for sustaining the on-station presence and duration of combat and non-combat warplanes in warzones.
Frankly speaking, I highly doubt that any pilot would like to spend 30 minutes, 1 hour, 2 hours or more just to travel to and from friendly bases just to be refueled, even if the mission zone isn't far away. That would be wasting precious fuel, airframe lifespan and time for nothing to gain for - Which is why tankers are fundamental to tackle these shortcomings.
For perspective - Operation Desert Storm, which takes place for one month plus, requires more than 200 tankers to be deployed to the region to support the campaign, even when many friendly airbases are right next door of Iraq in countries like Saudi Arabia, Kuwait and Qatar.
Try emulate that Desert Storm, but across much of the entire WestPac with much larger air forces (both allied and opposing), alongside much more demanding, intense and encompassing combat operations and missions. I believe you can figure out just how many tankers are needed for such scenarios.
And we haven't yet talked about the Himalayan frontier, which both the transport and tanker variants are equally important.