Well first things first you need to figure out what you want to do with the tank and how far you want to take it. I think a moss wall would look good, but are you going to keep the bare bottom? If you are you could always add some large driftwood and tie moss, java ferns and such to it and that should help the look. If you want to really get into it then get a good substrate, ferts, and a pressurized co2 system, as I see you have a good amount of light to work with. Get a better handle on what you want as the finished product and we can go from there.