When do I formalize my idea into a corporate entity?

I’m a programmer with an Idea. I have a working demo. I have the funds to cover hardware, bandwidth, software development cost, ect. I am currently doing most of the development myself, using Odesk hires, and hiring friends for contract work, with no formal contracts.

When do I need to get formal with a corporate structure? Is it really necessary to incorporate? Or, can I keep track of the important paper work for taxes etc., myself? Is there such a thing as a part-time business lawyer? Who else do I need to hire right away to help me with these processes? Should I use my first employee to fufill these business “process” needs?

Please submist your suggested answers or advice as comments to this story.