Whether you need a degree depends very much on the country's visa requirements. AFAIK you don't currently need a degree to work in Thailand. This may change though.
TEFL certificates are different and some are more recognisable and accepted than others. If you are serious about a career in TEFL (as opposed to just wanting to spend a year living and working in another country), you should definitely consider doing the CELTA or the Trinity TESOL. Online TEFL certificates are less valued and less recognisable, although that's not to say that you couldn't find work with one of them. Their main selling point is that they are considerably cheaper than a CELTA or Trinity TESOL.
Having some knowledge of your students' L1 is useful (as it helps you to understand why they make the mistakes they do), but it's in no way essential.
If you're not fussy, I imagine you would be able to find work somewhere. Thailand is a popular destination though and because of this, wages are generally low-ish and working conditions are not as favourable as in other places.
Don't go into TEFL for the wages! I've gone from earning 42K pa in my other life (graphic designer in the UK) to under 11K as a teacher. That said, the cost of living in Portugal where I'm working is much lower than in the UK.
Any more Qs, please ask.