If you would like to go with less sand, you can easily add a plenum this will help lower nitrate levels, and should eliminate the need for a skimmer. I ran a 20 gal mini reef using a plenum 2 inches of cc, 2 inches of ls, and 30 lbs of lr.
I had 2 powerheads and no filters. I also didn't feed the fish (2 perculas). I just let them eat what was in the tank.