If you´re thinking about setting a fish only tank, dead rock should suffice. You can seed the rock with some sand from another tank (maybe a friend´s or from your LFS).
One tip, you may want to trade those damsels in the near future, if you want to stock your tank with other fish like tangs, buttrflies, etc. Damsels are very mean to other tankmates, in general. Mostly if they´re the first residents. They can be real bullys.
You may want to read about fish you want to buy, to get familiar with particular dietary needs and husbandry (take tangs again for example, they are algae grazers in nature, so they´ll need a consistent supply of sea weed, and also some special dietary suplementation to keep their color and health). Also, you need to get familiar with specific water quality for the fish you want to keep. Some fishes are more sensitive to wide pH changes, for instance. You may want to find out about what fish is more tolerant to water quality fluctuations (another example). That may keep you from wasting money in expensive fish, and going thru a very much frustrating experience. Plus, you won´t sacrifice an animal over miseducation (I mean this in the best way...We have to think responsably about those little animals). So, for many many reasons, It´s good that you investigate about the fish you want. It can also help you plan better your aquascaping (like, to have enough space to swim for fishes like tangs, for example). Tangs are a good choice for a Fish only or for a reef, BTW. I love them !!!
I hope this helps a little!