for a decent spectrum the light really should be power compact. Which I believe is set for the one in your e-bay link. Which is decent for a tank that small... I wouldn't try
SPS's or clams, but most LSP's and mushrooms should be OK under those conditions. You can get 50/50's at 24 watts in that size.
As far as the sump goes, it's not necesary but it helps. Increases water volume which allows for accidents more than anything. The most important thing with a Nano reef that small is it must be topped off daily... a few ounces of evaporation will change the salinity! And water changes have to be very regular because DO's will built up fast!
Aside form those few facts a nano can be an awesome time. And a lot CHEAPER than a huge reef system, eh?
p