That tank will never look nice or support anything long term without enough rock. You dont have to add live rock, you can add dry rock (cheapest place to buy is MarcoRocks Aquarium Products ) and it will become live in a few weeks, but you have to have enough rock. I would aim for 5-10 lbs for your tank. The rock is where 99% of your filtration happens and where all the other beneficial organism live. You cannot have a successful, nice looking tank without good filtration. Order the rock ASAP before you crash the tank. Feather dusters reproduce sexually I believe, so you are going to have to buy more feather duster if you like the big ones. The smaller ones seem to populate a tank just fine.