I'm sure your tank seems empty now since all the fish are small, as they grow you will have some bad fights. You should prepare ahead if you intend to keep all those fish. Find people who will take the fishes that are abusive or being abused when it happens. Good thing all those fish are pretty tough and can withstand quite a bit. You might be able to keep 2-3 of the killers together successfully with the plecos if you're really lucky. There is no way you will keep all your fish, imagine having 10 footlong fishes in your tank, 8 of them being quite aggressive. 75 gallons isn't that much, this is MFK!