One quick question on email marketing

I started to build my own list(single opt-in) about one week ago, basically by following a post here on Making Money section: build a promising landing page and then send targeted traffic to it.

I want it to be 100% legit so I took some time to read CAN-SPAM act but still got a little bit confused, I've already rented a P.O. box in the US and my question is, do you still have to start a "real" business(registration and tax stuff etc.) to do email marketing? Or would it be OK to just do it with a simple website?

If you are just starting, I think it would be fine to start with a simple website and a PO Box address.

When I send email to my subscribers (from various countries), I even use my address (non U.S.)

That should be fine as long as your list is opt in.