How good you are and how many customers you have will decide of your income.
Some makes OK incomes and some have very good income.
Some just survive.
Like any business, you generally get out what you put in and the location of your business is also very important.
I believe that you questions does not really have an answer, to many variables.
An other important factor, may be the most important, is : how good business man are you?
You might be the best craftsmen but a lousy business man, if so you will starve to death.
I know by experience that I ma not a businessman, this why I will never start my own business to live off it.
I believe that those who make a good living of wood working are the exception. Where I live the competition is crazy and it is very difficult to make a decent living, yet I know two persons who makes an OK living of cabinet making.
Another consideration is that when you own your business, you work 24 hours day ,7 days a week .Are you willing to that?