You become a Business English teacher by teaching some people and preparing so well that your lack of expeeience doesn't really show and doing that over and over again until you know what you're doing. Fake it 'til you make it. If you want to know more about visas and transferring and changing categories I'm the wrong person to ask. I strongly suspect that shifting fields like that violates the letter of the law. Go ask in shanghaiexpat's visa forum/thread. If you can code factual.com seem to always be hiring if one looks at tgeir HN who's hiring thread history. Or perhaps email one of the people at techyizu.org. The local startup scene is their thing. IIRC meetup.com has a few relevant groups as well. Feel free to say if you learn anything in comments.

Thanks for provoking me to write this.