I think it is not really so important to have a CELTA or TESOL if you want to teach in China. Many universities will require you to have a degree however ( most )

The only way you will learn how to teach in a foreign environment is by experience, and CELTA is not very useful in that regard IMHO. I think it is better to pay a teacher or former teacher to help you on a one to one basis, show you how to do a proper lesson plan.

I will also add that at many public universities in China there are no textbooks for the foreign teachers, and also no AV facilities in many places, so you can't use PPT( Some newer unis have modern technology ) So in that sort of situation you really need to know what you are doing ( I am in that situation ) , and only experience will help you in such an environment.