My 4 blue reef chromis chase each other around quite frequently, in fact I suspect they offed the 5th blue reef that I had. They are really cool to watch though, very active fish, even at night with the lights off they are swimming around. They eat everything too,flake, pellets and frozen.
I ordered medium ones from Liveaquaria and mine came in at about 2 inches or so each so keep that in mind. Not sure how many you can fit comfortably.
Beautiful fish though and nice pick.