If the returns are placed near the skimmer then floaters will stay away from the skimmer. I accidently did that a while back. Sure seems like it would destroy the surface skimming but I didn't notice any build up at the time. Putting a *loose* screen around the skimmer box at the water level keeps floaters away nicely. It isn't attractive but probably looks better than a floater corral.
Placing the skimmer box at one end of the tank makes for a far cleaner display. When I took the background off my 5' tank I was able to move it to the end and it looked great. I cannot do that on this acrylic tank and it really makes a difference. I love jcdg's set up, external is even better......
My drain area grows fish. It turns out there isn't much turbulence in there at all and lots of food as debris collects on the sponges and grows lots of goodies. Surface area is still as the drains dump under the surface. If I pull out the heaters and take off the drain tubes it is easy to catch the fish. My sump just has drain area with large area for heaters, sponges [mechanical and biological], return area with no permanent dividers. In retrospect i wouldn't turn down a couple of dividers that would force water through the whole sponge area however.
Currently my second pump is in the tank under the internal HOB skimmer box with a spray bar located at the far end of my very long tank as I was concerned about stagnant water under the box. What if one pump's return either was a spraybar with a hole near enough the top to act as a siphon break or was divided with part as a spray bar and the rest just a nozzle return? I doubt you want a nozzle at the substrate level!
I suspect returns and drains at one end of a normal sized tank works fine IF you have the 10x flow suggested. I don't have that and am more comfortable with returns and drains at opposite ends of my 8' long tank. In the 5' tank with ~3x you could see stuff just floating down at 4' from the return so I had no faith that water was moving at the far side of the glass at all.
Shrimp will demolish the debris. My sump had the usual build up of mulm on the bottom, put some cherry shrimp in and it was GONE.