I’m not sure about renewing a previous teacher certificate. It will depend on the laws of the country you are. I’m sure that having this certificate will be great for your career.
Actually, I've never even needed it when applying for a job here in Taiwan. Although, whoever saw my resume may have thought it is worth something. So, yes, they will appreciate the certificate in Taiwan, but I've never seen where it is absolutely necessary to have. I originally took the online course before I went to work in China.
After checking out their website, it looks like there are no requirements prior to enrollment. They do suggest participants to obtain at least a high school diploma. You can get more of your questions here: https://www.uni-prep.com/tesol/tesol-certificate-faqs#faqnoanchor Hope that helps!
The certificate is recognized internationally, so it will definitely make teaching in China and Dubai a possibility! Here's the link to get more of your questions answered: https://www.uni-prep.com/tesol/tesol-certificate-faqs#faqnoanchor
Maybe you can but it would be best to ask some schools in Japan what they prefer. In Slovenia I asked at the place I want to work and at first they said they want the TEFL course but then I asked if the TESOL course is OK and they said yes.
This certificate is internationally recognized!