Please read the post below (or maybe above) "Info from an Asian American teacher" by Tamdoankc. I've met him and if he was a European looking American he wouldn't have had any trouble finding/keeping a job. Comparing your writing with Tamdoankc's, I would to say that you would have a MUCH more difficult time finding a job than he did.
I'm dissuading you (look it up) for your own good and the good of the students and their families. They pay a very high price for foreigner teachers and deserve someone with better speaking skills than their Vietnamese instructors.