The basics are you need an upstream connection (preferably one that allows resale), a way to connect to your customers (this was easy in the days of dialup, could be easy or hard with RF depending on details, and is probably hard if you need to run a hardline), and a router or something and billing software.

You only need paperwork if you're in a paperwork heavy society and/or if you're going to use public right-of-way to pull cables.