I have a BA in English, and an MA in Linguistics besides the MA in teaching ESL. I will have taught 100 hours independently when I graduate.
Depending on the country you refer to as abroad, for Canada and The United Kingdom you'd need to achieve at least overall 7 bands out of 9 in IELTS, whereas, for Australia, New Zealand and The United States of America, you'd need overall 89+ score out of 120 for TOEFL.
Yes! You will mostly likely need a TEFL certificate to remain competitive in the ESL teaching market. Most Asian countries are hiring ESL teacher on a high demand. Having teaching experience isn't good enough to get yourself exposed in front of the big companies. A combination of advanced education and experience alongside certification will get you a stellar job as a ESL teacher.
I am TEFL certified, most schools require a TEFL certificate, so I would say yes. Also, a TEFL certificate makes you look more credible.