The name of this music from the Grand Theft Auto Online Christmas tree

JP are indeed job points. As of now - they are used to determine tiebreakers. They are shown in the list of players and reset to 0 after every session.

There currently isn't a way for a crew to share property. You could all give money to one person to own an apartment you could all go to assuming that person was online. There is no practical way to share a garage as any vehicle driven into a garage becomes a personal vehicle of the owner and they can only have one personal vehicle out at a time.