What does that mean, "I want to make my career with udemy"? Does this mean you want to work for Udemy? If so, send them your resume. Does this mean you want to sell so many courses that you can be an instructor full-time? If so, the odds of this happening are almost 0 percent. Sure there are some instructors who are able to do this, but VERY few.
Let's say you lived in the United States and needed to earn $60K per year to live the sort of life you want to live. The average instructor earns between $1 and $5 for each course sold. Let's be optimistic and say you can earn $5 for each course sold. You will need to sell 12K courses each year. I have no statistics to back this up but I would guess that less than 1% of all instructors on Udemy are able to do this.
Yes, I agree that if you want this amount of money, it will be very difficult. However, some people don't live in the USA and just need U$600-1000/month as a primary source of income, and I believe this is way more feasible.