Hello Violetta,
What it means to become a yoga teacher is your first question.
To become a yoga teacher means making a commitment to slide one’s ego out of the way and fully embrace the mission of guiding others toward the light that dwells within. Said guidance should be as safe and as effective as possible.
It means committing to a path of constant re-evaluation of self and subsequent change, but not for the sake of change.
It means dedicating one’s self to integrity in teaching and therefore both practicing what one is teaching and not withholding tools from students. At the same time teaching relative to the student’s level of experience or context.
It means doing something each day to be better at your chosen profession. It means living yoga throughout your daily life. It means becoming an expert in the branches of the practice. It means understanding that yoga is far more than postures, adopting that understanding into one’s own practice and sharing a robust practice with others.
It means learning to be concise in communication all the while honing the skill of listening. It means refining thought and words so that instruction cannot be misinterpreted. It means refining the qualities of your voice and delivery. It mean learning to both see and look.
The process can be radically different depending on the level of sincerity of the student and their subsequent commitment. I personally believe that 200 hours of a sound training is a bare minimum. Sadly, many believe they are masters after 200 hours and some abilities to do things with their physical body. Nothing could be farther from the truth.
If you have refined your sense of awareness AND continue that in the teacher training you select, THEN you will know (inside) when it is time to teach, how, where, and so forth. You will also, most likely, understand that your training must go on, and on, and on. 
Physical abilities has very very little to do with the term “advanced”. An advanced student is one that can maintain a focus and use their consciousness inside of the posture. It is a student who does not need to be told to breathe. It is a student who is facing Yama, Niyama, and Kleshas AND doing something about that confrontation where it is required for "progress.
Being able to balance on your thumbs ONLY means you can balance on your thumbs. It is not at all a barometer of a proficiency in Yoga - though it certain can have benefits when speaking ONLY of asana.
If you choose a sound training there should be a business course that directs you in how to use teaching in order to earn a living (or “survive”). Applying to studios or gyms is a fine way to go IF that is what is truly in your heart (please see “honing awareness” above). Usually this invloves an audition though if you study someone reputable you may find an opportunity there when you are finished with the 500.
To open a studio is an entirely different conversation. That is a conversation about running a business and all that is involved. It is, for me, a thread of it’s own and perhaps covered within the ethereal walls of this forum in another location.
gordon
