What legal structure you will setup depends on various factors depending on your place of residence and business. I can’t give you advise (We are a Indian Private Limited Company) without knowing your place of business. Here are the things to keep in mind though. (Ordered by approximate order of importance)

• Does it minimize your taxes payable
• Does it have not-too-onerous accounting and reporting requirements
• Does it allow you to deduct business expense easily
• Does it allow you to additional equity holders
• Does it allow you to close the legal entity without too much hassles.

As soon as you have the legal entity, I suggest opening a bank account for this. This allows you to keep your personal and business account separate from start, and keep all your tax deductible expenses at a single place.