When I first started ESL in Hong Kong I didn't have any ESL qualification. I started the i-to-i Certificate after taking on students in centers. In China, if you have a little experience (which you can bluff your way into at first), then you can jump from there. That said, if you want to land an actual job as soon as you land in another Country, the ESL cert. would be helpful.
I found many people went down a certain path. They worked in a few Educational Centers, did a few after school programs through an agency in a real school, took on a little private tutorial before landing a job in something like a Kindergarten. I don't know about other places, but in Hong Kong it seems you can get a job in a local (not International) Kindergarten fairly easily.
You'll probably get snapped up by an agency pretty quick. They'll take a percentage of your income and own your working visa. This is not a bad thing, but if you find a job with a school you're better to drop the agancy. If your working visa is through a school, you can do a bit extra outside school (even with the same agency), and no-one'll be grabbing comission or leveraging you because they'd have you by the balls with your visa.
Educational Centers (in Hong Kong anyway) are busier on weekends and after regular school hours. This is sad because it'll keep you busy when your friends are going for dinner, and take your weekends. You can do them, but I'd only say yes to weekends if you NEED the cash. Kindergartens, or any school that'll employ you (maybe even an International School in some cities) are great because they'll offer you school holidays. WO!
Your face will be your main qualification. Any place in the world who is in a position to pay someone with an online certificate in ESL an okay sallary will probably choose you because you "look" like an English speaker. That means, they want you to look like an English speaker. I can't answer for everywhere, but it's certainly true in China, including Hong Kong. In Hong Kong an ESL certicicate holder wont get jobs in Secondary Schools or International Schools, no-one's that naieve to employ such unqualified people in well paid positions. I did know someone who landed a position teacher English at an International School in Shenzhen (China) though. If you can get away with it in Shenzhen, probably no problem in many other mainland cities.
In conclusion: If you can, get paid holidays. Too good.