As a single person consultant, should I incorporate? If so, as an LLC, C-Corp, S-Corp, other?

If you will be making agreements with other parties who are willing to contract with your business entity rather than you personally, then you would be better off forming some form of limited liability business entity. An LLC or for profit corporation will provide the same amount of protection. A C corporation and an S corporation are the same thing provided all the shareholders are US citizens and there are less than 35 of them. An S corporation is generally taxed like a partnership (which itself pays no federal income tax and all of its income and loss pass through and must be shown on the owners' personal tax returns) and it achieves that by filing an election form with the IRS. Nowadays corporations can be taxed like an LLC and an LLC can be taxed like a corporation so it doesn't make too much difference; it all depends upon an election made with the IRS. Both require a minimal amount of annual paperwork in order to keep the Secretary of State from administratively dissolving the business entity. Generally a limited liability company is more flexible and requires less paperwork than a corporation as it is not required to have bylaws or to hold annual meetings or take minutes at such meetings. The Washington State registration fee for either type of business entity is less than $200 and the annual fee charged by the Department of Licensing is $59. You may want to talk to your accountant to see if he or she has a preference for the type of your business entity. Based on the little I know about your operation I would recommend a limited liability company.

Your questions implicate both legal and tax issues. From a legal perspective, it would generally be advisable to form some sort of limited liability entity from which to operate, especially if you will be hiring employees in the future. This will provide a certain level of asset protection, if you observe all the formalities of forming and maintaining such entity. Having a comprehensive insurance policy, however, is even more important. Notwithstanding the foregoing, you may be held personally liable for your own actions, which makes the limited liability issue somewhat of a moot point. While Washington tax law generally treats all entities the same for purposes of Washington excise taxes, from a federal tax perspective, each of the entities you have mentioned entails different tax treatment. Therefore, it is advisable that you consult a business/tax attorney to evaluate which type of entity would be best for your particular situation.