Question about home based tutoring. (rush!)?

Hi, I am currently teaching someone else piano at my home, but my friends told me that it is illegal because I dont have any business license and certificate of piano.

Therefore, in order to be a tutor of anything at my own place,
1. do i have to get a business license?
2. do I have to have a certificate of "X"? such as "piano","math",etc
3. If it is not illegal, can I teach more than one student at a time?( do they consider it to be a class rather than a tutoring)

I am earning like $10 per hour, and about 10 hours a week,
can any professional tell me anything about it?

Thanks u all for coming it ! hv a great one!