All fine, see below

traveling outside US while H1B extension is pending is irrelevant to its approval. Which means you can wait in China and get a H1B stamp from consulate. See below:
http://www.murthy.com/arc_news/a_trh1b.html
http://oisshome.wustl.edu/immigration/h1b/TravelGuidelines.html

Your AP will be still valid if you use H1B for reentry.
Make sure you bring 485 receipts with you when passing through CBP. In some cases, they ask for them.
You might probably want to have FP done before your travel.