Five blue-green chromis were the first fish in our tank ... nine months and going well.
I find our chromis to be peaceful, at least to other fish. There's a little bickering going on between them (Pecking order stuff I imagine), but it only amounts to occassionally darting at one another. Nothing that would constitute "Fighting" or a danger to each other.
They're also fascinating fish with their schooling, color changes, and the way they swim ... they don't use their tailfins, just their pectoral fins for locomotion, which gives them some amazing manueverability. They can move forward, backward, straight up, straight down, much like aquatic helicopters. Also very adept at getting into teeny spaces ... all five will hunker down for the night in nooks that don't even look big enough for one, let alone five.
Also fairly smart ... by their third feeding they had figured out that that big, ugly, pink-skinned, two-legged thing was the source of their chow.
I wouldn't go many more than five, unless you have a really large tank.