You seem to have a lot of questions about your new teaching career. It can be confusing at the beginning. I will answer your questions in two separate postings. Here I’ll deal with your studies and in a future reply, I will deal with preparing lessons.
First of all, I think it is important for you to be clear about exactly what you want to study.
A 20-hour course is very different to a degree in TEFL. Most 20-hour courses take place over a weekend and participants learn the basics of teaching; for example, how to plan a lesson, how to manage a group of students, teaching grammar, teaching speaking etc. A degree is very different, a Bachelors’ degree usually involves three years of study (unless you are exempt from one or some modules). A Masters’ degree is usually one year full-time study. In order to get onto a Masters programme, you usually need a Bachelors’ degree and / or teaching experience. A Masters’ is more technical and theoretical than a weekend course or a TEFL certificate. TEFL certificates and weekend courses usually cover practical issues of dealing with a class. A TEFL certificate can be done part-time over one year or through one month’s full-time study. A Masters is often focused on the theory of language and language acquisition. Many Masters are offered as distance learning courses.
One thing to consider if you choose an on-line course is the amount of observed lessons that will take place. You should ask this question when enquiring about courses.
I can’t comment on the individual courses. It is for you to decide which suits your learning style and budget.
Good luck ,