What should I know about "informal" self-employment?

Two things:

1. I’m tired of being broke.
2. I keep failing those goofy pre-employment quizzes that jobs give you before they hire you. You know, the ones that are like “If you knew someone was stealing from the company, would you A) Tell your manager or B) Call the FBI. Oh you chose A? I’m sorry, the correct answer is B. No job for you.”

With that in mind, I’ve decided to take full advantage of the pseudo-capitalistic system and put my myriad skills to work in exchange for delicious monies. I’ve already been hired out to give guitar lessons, and I’m currently designing a logo for an up and coming home inspection business. The issue here is that I have a number of services I’d like to offer, but I want to consolidate them under the umbrella of a jack-of-all-trades/independent free lance contractor-designer-laborer type thing just for convenience and identities sake.

The problem is that I have very little business acumen, and I don’t want Uncle Sam to come skullfuck me because I made too much money or didn’t get some goofy license from the city county building before advertising that I can clean pools.

This is where you come in, Fluther. Are there any inherent problems to me just coming up with an informal business identity and hiring myself out to provide random services within my skillset to voluntarily paying customers? How much income can I make before Uncle Sam wants his share? Do I need a business license? What are some good ways to advertise my services or to network?

Thanks in advance, dearies.