This is assuming US.
You don't need to register for tax reasons. When doing taxes you report that income on, I believe, Schedule C form (which corresponds to a line in 1040 Form). Creating a company (LLC or S Corp) will cost you a bit of money and a bit of additional accounting/tax hassle.
As to people suing you.
A lawsuit would cost at least thousands of dollars in lawyer costs. No sane person will spend thousands of dollars to recover tens of dollars (or whatever your newsletter would cost).
Not to mention that unless you clearly defrauded them, they would not win. "I don't like what I bought" is not a winning legal argument.
The worst that can happen is that if they paid via credit card they can issue a chargeback through their bank. Which is why if you have angry customers that are not satisfied with your product, refund them quickly, no questions asked.
You don't need terms of service. In practice they'll not make any difference.
If you really want some meaningless text on your website, you can pay a lawyer, use a services that sells cookie cutter TOS or copy TOS of someone who does a very similar thing.
