I like the idea, but IMO, having a 2.5g sump is pointless and a hassle for a tank your size. You'd be better off not having a sump and running a medium/large HOB modded filter.
As for lighting, you really only have a couple options as there arent pre-fab fixtures that will nicely fit a standard 5.5AGA. Your best bet would be to do as dtd said and build your own little LED array and mod it into a desk lamp fixture (would be sweet) but I was going to mention, if you have about 80$ you can spent on a light, you could always just go buy a par38 bulb, which would be perfect.