What characteristics do you think a good English teacher should have? For example, do they have to be a native English speaker, or is this not important to you? Do you think an English teacher needs to have different characteristics from a teacher of another subject?
For me, a good English teacher mustn't be a native English speaker. As all teachers, the first quality is to like to teach. More than the other works, an English teacher must be enthusiast by his job. But I don't think an English teacher is different than an other teacher.
Before answer you I have a question. In United States or in Great Britain or in Australia, the English spoken it's the same? The grammar rules are the same? And moreover, what is the correct pronunciation, perhaps is it the 'Oxford English'?
Regarding your questions, there are a few different grammar rules among these countries, but in general things are the same. Of course, expressions, and idioms are different from country to country.
About pronunciation, there is no "correct pronunciation". Each place or country has its specific way of speaking things.
Hope it helps you!