I would say the skimmer output needs to be away from the return pump to help keep bubbles at a minimum. I have always had mine next to the drain line but don't think it really matters.
As for sand, some macro want to root into sand but chaeto does not need it. I have 1-2 in of sand in mine but my tank sand is 3-4". Some put a DSB
in the fuge if they don't have one in the tank. Again, really does not matter. Pros and cons to each. DSB
has worked well for me so far.
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,