Add a pair of cleaner shrimp. Consider smaller brittle or serpent stars too. Also, look at sand burrowing snails to help with the sand.
Now, you got the chromis and plan to get the pair of clowns. They'll all swim out front, so now concentrate on something that'll perch on the rocks higher and lower.
For the higher, you got planny choices such as the black sailfin, midas (both larger get larger), and bicolor blennies that perch high. Other blennies like canary and other fangs also swim out front and don't perchm, but interesting characters anyway.
For the lower, you got all kinds of gobies to choose from. Some shrimp and others not.
BTW, my sixline didn't eat prepared foods and starved in my early tank days. Just seemed to cruise for pods
. I'd wait some time before you add him.
Can't go wrong with blennies. Very amusing and interesting character IMO