I have a 90g with three in it. They are pretty docile and don't move much unless your feeding them but then all bets are off.
I recommend if you get more than 1 you try your hardest to get females and one male.
The easiest way to tell their sex, although its not fool proof is to pick out the biggest ones.
Next check for a white stripe, If they are fully grown and have one they are most likely female.
Second thing watch them, if they frill out their neck and it turns red, plus they do pushups(you'll understand when you see it). Then most likely they're a male.
If they have stubby noses compared to the others in the tank they are most likely a female.
These aren't fool proof ways to identify them but when put together you have some pretty good chances. However they can throw some curveballs.