I read somewhere that the Sopranos are based on the DeCavalcante family of New Jersey... Are they a single Mafia family, or a branch of another Mafia family? I ask because in series one of the Sopranos, Junior is made "Boss", and is labelled so on the FBI family tree. But in the next episode, Livia tells Tony how full of himself Junior has become since being made caporegime. I'm confused, was he made Boss, or caporegime? In the latter case, why is he labelled Boss, if he is only caporegime?

Yes, that is true, the fictitious Soprano Family is loosely based on the real-life DeCavalcante Family. Not the characters, but the power structure of the Soprano Family matches real life.

Apparently, their are six crews that make up the DeCavalcantes, just as their are six crews in the Soprano Family (Tony Soprano crew, Junior Soprano crew, Jackie Aprile crew, Barese crew, Curto crew, and the crew of the now-dead Jimmy Altieri).

Also, the DeCavalcantes are an independent Family with a free hand in New Jersey, but still answer to one of New York's Five Families when it comes to major decisions. I forget which one; I think it's the Lucchese Family that the DeCavalcantes have ties with, but I could be wrong.
And in the show, the Soprano Family is closely associated with the New York Family run by Carmine Lupertazzi and John "Johnny Sack" Sacrimoni.

"They're not a Family, they're a glorified crew" I think Carmine Lupertazzi said that. Which is basically true. They are a Mafia Family but in the New York scheme of things "They're a glorified crew".