Wish you the best of luck in your endeavor. I know nothing about being in an illustration business, but I know a lot about being in business for yourself in general.
Being self employed, whatever the business, takes a financial investment. You need to have financial support while you are building your business and that usually means a job to support the start-up business. I've started three business ventures in my life. One was successful at the get go, but when the economy went down hill in 2000 I lost my major client and was forced to take a job. Another try at a start-up failed miserably from the start and I was forced to close in one year. And my last venture was a money pit for the first four years that ate up everything I had plus put me into debt...however once it started getting profitable it took off and we (husband and I) were able to sell the business in 2010 and retire. So if you are a risk taker and can afford the highs and lows of any business and you have talent and are a good sales person of yourself and your product...you will do fine and be successful.