I'm pretty sure this is the first year the NBA has kept these stats officially. +/- is the difference in points scored by the team when a player is on the floor. For example, if Lebron James plays 40 minutes in a game and the Cavs score 15 more points than the Bucks during his 40 minutes on the floor, his +/- for that game is +15.
BA stands for blocks against. It shows how many times a player's shot is blocked during a game.
http://sports.espn.go.com/nba/news/story?id=5468878 This article reports that it is believed that Melo will not be on Nuggets this year. Of course they only bring up New York, but it is ultimately Denver's choice where they trade him.