Meditation teacher is my FI goal, I'll probably get yoga certified because I'm sure those businesses will be tightly coupled.

Do you think we need to be in specific kind of cities (smaller vs bigger) to earn a living doing such a job? Or do you think doing solely this is not enough to earn a living?

Location matters, but I also think it depends a lot on how you market yourself. A small mountain town won't have enough clients interested with the means to pay for those services. A resort destination (Hawaii?) could be really good. I think that is why I want financial independence though, so I can worry a little less about how much I can earn.

From reading it sounds like yoga teachers are plentiful since a lot of people practicing naturally progress to getting certified. Starting wages can be very poor because of this. That's where I think marketing can be the differentiating factor. Travel around India learning, maybe write a book or blog about yourself. Get on reality TV and become a minor celebrity. Have a very well respected lineage. Just some ideas to bring in more clients.

Big cities are definitely the safest.