When you work as a teacher (of English) you've got the next advantages:
1. You've got the opportunity to support your English skills. You have to prepare your classes, read books and refresh your memory every day.
2. Working as a teacher, you can be useful for lots of people. You can give them priceless knowledge and
just make them happy. You can help them to get more successful in their life.
As for disadvantages:
1. English is not native. Sad as it is, if you don't support your high level constantly you will start fading with your speech skills. It's difficult work to stay in a good condition all the time.
2. This occupation demands lot of patience. It's really hard to teach English people of all ages. This is an extremely nervous work. Because everyone wants to speak English fluently, but almost nobody wants to study hard.