With the IRS....depending on how you incorporate.....there are various tax forms that you may have to file. A small sole proprietorship can get by with the Schedule C included with their 1040. In this instance, they will require SSN....while they do not require a Employer ID Number (EIN) (but can be included if you obtain one). Again these are for small business that are borderline hobby and business.
The IRS concern is that you file the correct forms and that you correctly report income and expenses. They could care less about a business license. They'll want to make sure that you report under the EIN or SSN, depending on how you incorporate.
It doesn't hurt to consult a CPA and lawyer....to ensure you are set-up properly and to the most advantageous for your business. I'd have to refresh on prior knowledge, in order to help further. The IRS website contains a lot of information, if you are concerned with them.
IRS Small Business / Self EmployedA few things that you may not think of immediately.....
If you are self-employed you must pay Self-Employment Tax
Self-employment tax (SE tax) is a social security and Medicare tax primarily for individuals who work for themselves. It is similar to the social security and Medicare taxes withheld from the pay of most wage earners.
If you are self-employed you must pay Estimated Taxes
This applies even if you also have a full-time or part-time job and your employer withholds taxes from your wages. Estimated tax is the method used to pay tax on income that is not subject to withholding. If you don’t make quarterly payments you can be penalized for underpayment at the end of the tax year.