Can I take chinese currency into china

Of course, you can, but 20,000 CNY is permitted. If you have more than this amount, related documents will be needed and you need to declare to the customs.

What related documents are needed? Can I risk not getting the money in even if I fill in the documents?

How much can I take out at ATM's in China (Visa, MasterCard etc.)?

As I know, if you take more than 20,000 RMB out China, you need to get certain proof from a bank. But for taking much money into China, no documents are needed. Just declare them and fill in the declaration form. If get the permission of the customs, it is ok to come in.

I remember you can take out 2,500RMB evert time from ATM and it is allowed to take ten times with one card.