If it's real, it needs to be accurate. Mainly to avoid angry emails from the residents. If it's somewhere you haven't been, you could do enough research to get by, so long as you didn't make the town and its layout central to the story. Check out the pictures on the web. Contact a few residents if you think it would help. And most towns have a website. A picture of the streets and houses could be enough, again depending on the amount of detail you need to tell the story. If it is set in New Orleans, but the whole thing takes place inside a home, you'd only have to know the basics of the city.
As for people, I'd steer clear. Unless it's non-fiction and you have documentation to back up what you say about them, you could find yourself in a lot of trouble.