I think that separation is one of the hidden benefits of incorporation over sole proprietorships: It absolutely forces you to think of the business and your personal finances independently. A lot of trouble can occur when that line gets blurred.

As to the CPA question: you don't just need one, you want one. S/he will be offering you a lot more than bean counting. You get the advice you need to take advantage of the tax advantages of your configuration in a legal way, and its also an experienced set of eyes looking over your expenses and numbers. A good CPA is one of those expenses you really feel you get your value out of.