I have to disagree with Roman - less is not more when it comes to plants! :) I think a moss wall sounds lovely, and they are (theoretically) easy to make - just do a quick google. :) You'll need craft mesh, suction caps, and, of course, moss.
A moss carpet is also a fantastic, low-light way to carpet a tank. :) Google Acumen Aquatics and go to the gallery - she has a moss carpet tank that I have always been jealous of.
I would suggest getting a piece of driftwood to put in the tank and attaching a combination of java fern and anubias to it to create a little jungle.
If you are using organic soil, you also need plenty of fast-growing plants to prevent an ammonia spike as the soil breaks down. Try hornwort, anacharis, wisteria and lacefern. Check out OFL's amazing NPT thread as well (stickied) for detailed instructions and plant recommendations. Floating plants are also great - duckweed may be a pain for us humans, but my bettas love it.