No worry...

1, Is it ok for me to visit China without AP?
Yes, 100% safe. Nobody will mention A/P to you.

2, If it is ok, do I need to have I-485 receipt with me.
No. I have been in and out for so many times in same situation. Never was I asked for the receipt. As a matter of fact, the border entry system does not even show you are 485 pending
3, Any additional documents I need to have with me.
Nothing else except those you know you should