if you're using a huge algal turf scrubber then you don't need to worry about a skimmer. but other then that you should use a skimmer. once you see what a skimmer takes out of a tank you'll never live without one.
on the sand bed issue. a deep sand bed will help remove nitrates from your tank and my nitrate levels usually hang around 5 ppm. the way you do it is make a layer of sand about 4-5 in and seed it with live sand to make sure the sand has some movement in it. there is a hypoxic (low oxygen) zone at the bottom of the sand where bacteria grow that remove nitrates from your system. definitely worth the investment.
