First, Steve hit the most important point - you work to support your family, and they come first. For you to make a go of it, they will be making sacrifices too.
Form an LLC or a sub-chapter S corporation to separate your personal assets from your business assets.
Get some good accounting software, learn the principles, and be absolutely anal about GOOD RECORDS.
I ran bare for years, but times have changed and Steve's comments on insurance are accurate. Almost all clients now require certificates of insurance. (Damn lawyers are ruining the country.) I did always carry workman's compensation - that is law in most states.
Be prepared for swings of the pendulum. Good times and bad will follow each other with regularity. Don't get discouraged.
Make it your firm, unbending policy to never accept projects that you are not qualified for. It is tempting to buy some groceries when you think "I can probably do that" but in the long run it won't be pretty.