Green Chromis School

My wife is set on getting a school of green chromis for our tank and now she is trying to find other fish that would also join the school.   So far we know that we're suppose to have an odd number and we're thinking about 9 fish for the school.
Does anyone have any advice as to what what other fish can join in this school and any potential downside of having this many chromis or a mixed school like this?

Thanks!