@Ranzo The first name thing has to do with the way Japanese language/culture works. The closer you are to someone and the more you get to know them, the more casual your language is with them. And the way you call them has to do with that.
Using "FamilyName-san" -> "FirstName-san" -> "FirstName" as a standard: Acquaintances or just casual friends would use the first, closer friends the second, and your best friends/family would use the last one.
Tl;dr it's a bigger deal in Japanese culture to use given (first) names than it is in most Western cultures because it shows how close of a relationship you have with the other person.
I hope this was helpful and not too long!