Freelance programming - do I need to register or get a license?

Do I need to do anything official such as register with the state or setup some separate bank account to be able to do freelance programming and accept payments?

I searched and read that unless you incorporate you will need to report taxes as a sole proprietor. Do I need some legal stuff to work as a freelance programmer?

I am located in the US, and have a green card. I have a fulltime job and am looking at doing freelance on the side.