Your situation is a little unusual, and I can;t answer with 100% certainty that your undergrad work will be sufficient. However, I think it would at most schools, if you already have your bachelors degree (if I read your message correctly).
There is no hard minimum GMAT score. Don't let anyone tell you otherwise. If I quoted you a number, it would be almost meaningless. But yes, a strong GMAT score can help overcome a low undergrad GPA. Just try to at least be within your target school's middle-80% average GMAT range (most schools publish this info).
If you want to pursue a teaching career, you may want to look at PhD programs. Very few people just get an MBA (or other masters) and then go into teaching.
Re: being in the U.S. now, that doesn't necessarily help or hurt. But being able to fund your education can help.
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