Ji,

I presume you want to know whether you need to organize your business as an LLC or corporation. It is generally recommended to consult an accountant (for all tax related issues) and a lawyer (for all liability and corporate law related questions).

Off the top of my head I would say you don’t really absolutely need to incorporate or form an LLC, because you are a single owner and your business probably has very little risk. Still you should consider the benefits of formally organizing your business.

As far as EIN goes, you might not need it at all if you stay a sole proprietor (or even form an LLC if you are the sole member). However you would need it if you incorporate.

Sales tax – you do need it if you would be selling any tangible property to end users (as a retailer), which I think you would.

And finally, one (almost anecdotal) advantage of choosing to organize your business in Maryland: its a real challenge to register a DBA in that state. The reason is most peculiar – since DBAs are registered with a town clerk you need to visit the town clerk office to do that. From our experience calling town clerk offices in Maryland is a futile endeavor.