What are the legal requirements for an online business? Business license? Business Tax ID?

In most states, business license is DIFFERENT from business registration.

Business license is typically required for businesses that sell alcohol, tobacco, day cares and other types of businesses -- but not online business.

I run several websites and all I was required was to register my business and file for a doing business as (DBA or fictitious name) if you will run your business using a name other than your own. For example, instead of using your name JANE DOE you will operate your business as SCENTED CANDLES GALORE or call your business as WIDGETS.COM OF ALABAMA then you will need to file for DBA.

If you will sell goods, you will be required to get a sellers permit. Wholesalers will require this and you can't buy wholesale without it.

I suggest you go to your Secretary of State website or your official state website (e.g. Alabama.gov) to check the requirements in your state. For example:

Starting a Business in Alabama http://www.alabama.gov/portal/business/s...
Starting/Forming a Business in Massachusetts http://www.mass.gov/?pageID=mg2subtopic&...
Starting a Business in South Carolina http://www.sc.gov/Portal/Category/STARTI...

I would get a business license at the local city or county authority. I don't believe it is necessary but they are usually inexpensive and it would look good if you were audited. You do not need to apply for a tax ID number if you are a sole proprietor. IRS will use your social security number . If you are selling goods that you purchase, you may want to get a vendors license so you do not have to pay sales tax on the product you buy.

Good Luck