You'd need to look at the Sticker behind the battery for determination of the correct Device Model Number. Sometimes the information you see in Settings > About is not accurate. The apps you'd use may get mislaid.
Having said that Since you bought in China, it is likely to either SM-G900I (for Asia Market) or SM-G900K/L/S (Korea Market). My Money would be on SM-G900I. Given that the device is so new, we do not have sub forum for this specific variant yet. But depending on which carrier you are using or planning to use, here are the links to Relevant forums. Sprint Galaxy S5
, Verizon Galaxy S5
, T-Mobile Galaxy S5
, AT&T Galaxy S5
To your question on Root, here's a nice thread
for Sprint S5. It gives you a general Idea. But understandably the specifics would depends on your Model.
You may also use Android Hardware Info
app or any other Device info apps that look at the hardware to determine Model Number.