That is an inflated number... Active duty is more like ~300. also US aircrafts are short legged and US cover the whole world... Chinese need is probably high double digits. Maybe very low three digits.
Well, based on the USAF, my understanding is that a single tanker can support 4 fighter-sized aircraft on a mission.
Hence 500 USAF tankers could support the 2000-odd fighters of the USAF.
For the next 15 years, the Chinese carrier fleet will still be significantly smaller than the US equivalent. Therefore China will have to rely on land-based fighter support to a greater degree and wants them to reach as far as possible into the Western Pacific.
In addition, longer-range fighter operations to the Japanese Home Islands will really benefit from tankers.
Given that the Chinese military currently has about 2000 frontline fighter or bomber aircraft, 300 tankers would only support extended range missions for 1200 aircraft at most. Call it 600 towards Taiwan/Guam and another 600 sorties for air superiority over the Japanese Home Islands.
Then you have to consider that inflight refuelling for existing and upcoming bombers will consume a lot more fuel.
And in the longer-term view when the Chinese Navy will likely field a larger carrier fleet than the US Navy, those Chinese tankers will still be useful for bombers, given the distances in the Pacific.
Hence my view that they'll buy at least 300 tankers