Write a proper business plan. You will learn all the things you need for a business, and what your hourly rate will need to be, and how many customers you need to make money.
There is no magic number people can throw at you. There are far too many variables per individual situation.
Having said that, you should be making a minimum of $100 an hour to "make it". This includes time spent doing clerical work, not just time spent with the customer.
Do you have figures for insurance, tax, wages, consumables, equipment...to name a few concerns.
Read this thread that people were REALLY helpful in.