You will know how much capital you will need when you assess your risk appetite and your strategy . Its not about spending $5K for a seminar to learn , just like do you think you can master a language by attending a seminar?
Let's say you are a seasoned trader (not expert), has consistent profits for years. Say you normally use about 20:1 - 50:1 leverage, how much capital do you think it's enough for you to quit your job and making a living trading forex full-time?
SO lets say that I am a season trader that has consistent profits, meaning that you are disciplined . Since I have been earning profit for example 3 years, and maybe the 1st deposit is $2K, and it has rolled to $61,825 using 10% compounding effect. Wouldn't it make sense that your portfolio IS YOUR CAPITAL?
But all this doesn't make sense when you are playing forex. In order to be expert, I reckon 5 years of constant training.
So stop dreaming to do full time forex if you have not played for 5 years with good results and no passive income to support down times.