I've taken your questions and I'll answer them one by one:
Now everywhere i look it says that english does not have to be your native language. So is that true?
Some schools and some countries will hire teachers who are not native speakers. Obviously, the options open to a non-native speaker are more limited.
i have a document that proofs that i have studied in the english school but is it going to help me at all and what good is it?
I suggest you check this out with the consulate of the country you wish to teach in and / or with the British Council.
Do i need a certificate or anything in order to take the courses and most of all-look for a job?
I suggest you check with course providers; look on their websites, call them up, etc. Check job ads for the country (countries) you wish to work in.
i've been thinking about thailand-how do you arrange your working visa-it's not a really hard work....is it? I guess that has more to do with my own government's agreements but still-someone might know.
I suggest you check with the Thai Embassy or Consulate in your country. You could also put a question in one of the open forums on this website. I'm afraid I don't have experience of working in Thailand.
As for your final comment on the lifestyle of TEFL teachers: there are many positive points to the work as well as negative ones. Sadly, this is the same for almost all careers. Only you can decide what you want: if you really want to teach English, have a go.