I always suggest that mandarins are avoided. They eat thousands of pods daily, to the point it is said that they eat one about every second. It is hard and expensive to keep them fed. I tried and failed, even with a mandarin that ate mysis shrimp which is rare.
I wouldn't add anything. I'd wait and watch, play it by ear. That is a lot of fish in the pipe already.
How deep of a sandbed will there be? Maybe a jawfish?