yup. i would get rid of the tang 100% without hesitation. next, if i were you, i would get rid of the damsels. yes, they look good for a bargain price, but will be aggressive. i have a 58 gallon, and am going to get rid of my damsel. looks nice, but way to aggressive. its personal choice there though, but you probably wont be able to get any more fish if you have damsels since they will tear them apart.
as far as rocks, you need some. once you get some rock in there, get some mushroom corals or kenya trees as they are easy to keep. you can just super glue the base on the rock, or ruberband it on to a rock. just do a search, there are great threads on how to attach a frag to a rock.
good luck to you
PS- Jacrmill has some good points. i thought i had the most peaceful damsel alive, yet, it destroyed my blue tang, and tried to harass my foxface. so its getting the boot. and all the other things he also stated are very true. spend some time reading.