A TESOL certificate is nice but definitely not required. Neither is a degree. An Associate's Degree works just fine especially if you have had some experience teaching back home. If you want more information about teaching in China you should check out this free online guide.

http://www.teachabroadchina.com

No, a TEFL Certificate is DEFINATELY not required. If you have a 4-year degree you are qualified to teach English in China. A TEFL Certificate will open a few more doors for you though. Don't get one of those fly by night ones though..
Be prepared to spend between $400-1300 Dollars on a good one.

You had better have got it, if you don't have it, they will check your college diploma to make sure you have finished the TEFL or TESL courses. in fact , most of foreign teachers in china don't have the certificate.

Yes you will need either a TESOL, TEFL or CELTA. You will also need a degree as it's a visa requirement there but not strictly.
Please see my answers here
http://answers.yahoo.com/question/index;_ylt=Ak3KmEbjDQ1PaZ9pnvho583ty6IX;_ylv=3?qid=20080308083631AAdfeTI&show=7#profile-info-AA10544698

http://answers.yahoo.com/question/index;_ylt=Ak3KmEbjDQ1PaZ9pnvho583ty6IX;_ylv=3?qid=20080224164042AAb1Mss&show=7#profile-info-mZDaxwuBaa

http://answers.yahoo.com/question/index;_ylt=Aj0KBRhR8OTZ9z3FyvOGAC7ty6IX;_ylv=3?qid=20080211105613AAJagoL&show=7#profile-info-wkk5jifzaa

http://answers.yahoo.com/question/index;_ylt=AjcTPAE7AlmdRPCTW0YQSnDsy6IX;_ylv=3?qid=20080308030946AALG3f3&show=7#profile-info-NRDxPojaaa

Best wishes
Z