I can't think of any material tax difference to him as a sole proprietor versus an LLC, and if you don't have an LLC, you don't have to worry about getting an EIN (can a single member LLC file under the members SSN?), setting up an LLC, drafting the management agreement between the LLC and it's member(s), etc. Further, if the OP is to be an "employee" of the LLC, there may be some unemployment taxes due, and workman's comp issues, that a sole proprietor does not have to deal with.
Although some states have fill in the blank online forms to create LLC's, corps, etc., AFAIK there is no such thing as a fill in the blank management agreement or bylaws and there should not be because they should be specific to the needs of the particular entity. They may not be needed for a one person LLC, or one shareholder corp. but one would have to know the law in a particular state to know exactly what is required to establish an LLC or corp. in that state. This is a long way of saying that just because there are some fill in blank forms available, one still needs to see a lawyer to determine if more is needed, lest one wind up confronting the issue of de jure versus de facto at an inopportune time.
I seriously doubt our OP need do more than take out a business license or registration in his jurisdiction and establish a separate bank account to make his record keeping easier, but he should consult a good accountant and good lawyer IN HIS JURISDICTION before making a decision.
To me, the concept of asset protection comes into play when you have multiple income producing or investment assets and you want to minimize one asset's exposure to liabilities caused by another. That does not seem to be an issue here, and the nature of the OP's work makes it likely that he would be sued personally for acts or omissions regardless of his business structure (it would just be an extra defendant), so I say make it no more complicated or expensive than necessary.
What piques my curiosity is why it is even necessary. In my experience when this goes on, a couple of factors can be at play. The hiring entity may be trying to pass off people as independent contractors in order to avoid exposure to the respondeat superior (liability for the acts of your employees) doctrine. Most states look to certain characteristics of the relationship to determine if one is an employee or independent contractor, and this can and likely does, vary state to state. Other times they are trying to offload employee costs by calling their employees something else. They can shed themselves of mandated benefits, unemployment contributions, and dump half of the social security tax on the "contractor". The IRS has its own set of guidelines on this issue and would likely take the state test into account as well. They like to see taxes withheld, and don't want to have to rely on people paying their own taxes.
I'm off to google "LLC".
