If you only have one circuit, and don't use a subpanel, you don't need anything other than what's likely there. Unless there's a very good reason to have a separate meter, it generally doesn't make much of any sense to do it for an outbuilding. A second meter means a second base charge, separate billing in addition to whatever electricity cost you might use...better to just run it off the main panel.
You can put as many receptacles on a single circuit as you want. You have to determine what you need, and what load there is. If it is larger than what one circuit will support, you'll need to run sufficiently sized new wire (a 4-wire circuit) off the main panel in the house out to a new subpanel in the barn. then, you can add as many circuits as you want, again, assuming your main feed is sufficiently sized. Then, you could shut the entire barn off with the breaker feeding it in the main panel, or out at the subpanel, individual circuits.
IOW, if done properly, you could add all sorts of lights and receptacles off a single circuit. You may not be able to power everything at once, but to get more than one circuit, you need a subpanel (or a completely new service).