I can see that you have many things to think about. You must be asking yourself a lot of questions. I’ll try to answer some of your questions and tell you about resources where you can find answers to the other questions.
It’s a good idea to get your certificate from a training centre that is certified and accredited. This will give you better and more opportunities to find a job. Whilst you can get a job with a certificate from a centre that isn’t certified and accredited, employers often consider the place where you got your certificate from.
For help choosing your course, you could look at the TEFL course database on Tefl.net. There is also a section called EFL FAQ on this website where you can see answers to your question about TEFL and TESL.
It’s quite natural for new teachers to be concerned about the grammar of the language they are teaching. However, as you say, you will learn techniques for teaching grammar on your course. Your knowledge of applied linguistics will also help you, especially with advanced students.
Concerning your question about repaying your student debt, I can’t really answer that, but there are some things to consider. If you’re going to work overseas, think about the exchange rate between that country and your own as well as the cost of transferring money between countries. You talk about the dollar, so I guess you’re from the US or Canada. If so, you could look into working in your own country for a few months teaching people who visit North America to learn English. This would probably give you a better salary and would allow you to have a first experience in a familiar environment.
I hope this will help you. Please write in again if you have any further questions.
Tefl.net can only give guidance in your career choices, we are not responsible for decisions made by individuals.