Ok...to start, how big are the filters you're running? If you have large enough filters, it's better to have more fish in a cichlid tank. Since they're so aggressive, putting more fish into the tank breaks it up into microterritories and the fish have to spend all day bickering with one another instead of just a few fish ganging up on one smaller one. If your filtration can handle it, you could easily put 20-30 fish in a 45 gallon tank. Checking your ammonia & nitrite levels will let you know how good of a job your filters are doing.

You don't have to cycle the tank again - just take the goldfish out.

Rearranging the setup in the tank is fine because once again, it breaks up established territories. Also, introducing new fish after lights out helps, because the others have gone into a less aggressive nighttime mode.

You do know that livingstoni are very specialized fish predators, right? He's likely to be the tank bully, especially when he gets big. Make sure there are lots of places for everyone else to hide, and seriously consider upping the fish load to prevent picking on one or two smaller specimens.

K