To buy IPhone in China

To buy one in China you will have to go to China and buy it from an Apple Store or Authorized Apple Reseller. It may have some limitations but to being targeted at the Chinese market and will have two physical SIM slots, not an eSIM and one physical SIM slot. If you need any warranty work on it you will have to return to China.

It should, but as I said if you need any repair you will have to return to China. If it is going to be a year that you are using it I would consider buying it, use it for a year, then sell it before you leave China and buy one in Korea.

Will you have a chance to visit Korea during your year living in China? If so, you should put a friend's Korean SIM in your phone and confirm that it works well. If it does work well, that will give you the confidence to bring your phone with you when you return home for good.