I wouldn't go with silica sand myself, it's too fine and gets really dirty. Something like play sand or construction sand is a little more forgiving and natural looking. Anything that's not black really. 4 T5 is heaps for a plantless tank, I'd suggest changing the tubes to something a little whiter, maybe 4000k-6500k (cool white-daylight).
Getting the tank to look "right" takes a bit of practice but will only work if you have the right materials to begin with. Some larger hardscape will provide a bit more of an impact if placed correctly. As Dennis said, stick to the rule of thirds.
And finally, here's a few tanks that might be suitable for you needs.
http://www.aquariumdesigngroup.com/data ... chlids.jpg
http://showcase.aquatic-gardeners.org/2008/show53.html
http://showcase.aquatic-gardeners.org/2009/show33.html