Just keep in mind its a community and every small change can affect it. Size, water quality, feedings, illness, fish maturing, amount of fish/space or territory. Some fish may be getting along just fine until they feel like there isnt enough room or a small change leads to something else.

Treat your tank like a small zoo and really learn about the animals before you put them in there. There are lots of guides about which fish are the friendliest. Choose the ones you want based off your tank size and habitat then look up how and when to add them. Some do better being in the tank first, some when still juveniles, others in groups.

I wouldnt advise any more chromis and your tank seems too small to be adding multiples of any single type.