S1 or L Visa

Hi, me and my girlfriend are hoping to go to china in August to work as teachers. She is applying for teaching jobs at the moment and with her qualifications it should be too hard. I am doing my TEFL in June and will then start applying for jobs myself but without a degree might struggle.
If I dont have a job lined up before we go, what should I do in regards to applications, should I come over on a tourist L and if a job comes available apply for a Z working type
whilst in china (is this possible?) or would it be possible to go to china on a S1 for private affairs when my girlfriend gets her residence permit and then apply for a Z if any jobs arise? - if this is possible would I have to wait for my girlfriend to get her residence permit in china before entering the country?
Is it possible to change the type whilst in china or would I be required to leave the country and apply again?
Any help would be greatly appreciated