Sump:
Well there are quite a few. I have never bought one so can not really recommend, for I was always surprised at the cost when it's relatively easy to just make one from a simple tank and partitions put in with silicon... but ok- if you want to buy I would suggest that most will do. If you plan on a Reef tank however, I would you get one without a wet/dry section (trickle filter or anything with Bio Balls). Properly managed they are fine, but can easily live up to their reputation as 'Nitrate Factories' when all your biological filtration should provided by the live rock. If it's a fish only you are thinking of - then the inverse is true = get a wet/dry section...
Thougths on sand: Well I am in the process of setting up again - having sold a couple of systems a few months back in order to move. I had sumps there with one section acting as a refugium = sand, rocks, macroalgae etc... I supplied light as is fairly standard.
I found a few things:
1) The light induced algae growth throughout the sump - not just in the refugium section, but also within my skimmer (which I have subsequently learned is undesirable)
2) I found that without regular maintenance (and even with) it just generally got messy down there.
So: if you are thinking sand and light to act as a refugium I would stress the maintenance and try to find a way to shield the other sections and equipment from this light.
In the small system I am currently setting up, I am leaving the sump in darkness, just installing the required equipment. I plan to have a refugium, but this will be at or above tank height to overflow back in the display tank = seperate and with a pump feeding it, not returning...
