Wall of tekst incoming:
Just some thoughts about this subject from my own experience. I build my tank and sump with discusfish on my mind, so it could cope with big tunrover rates and the sump had to be able to house a lot of media. I put in a divider (a glasspane glued between back and side thus creating a triangular space) in a backcorner to act as overflow and made a hole in the side of my tank to get the pipe in. The overflow was set so when the power cut the tank wouldnt drain by itself. Later i thought that i woudn't get enough circulation so i decided to add a hole in the lower end of the divider to get water from the bottom of the tank in the filter too. This gave the draining risk again, so i crafted and glued a small box over the sidehole in the tank (open on top and glued inside the dividerspace on the tank wall)) to act as drainsaver. I used some special plastic grate to keep fish from getting over the divider. Later on when i decided to get some smaller fish this was a problem cause very small fish could get through this. Seeing some fish behind the divider was a a pain because i could hardly get them out (deep and out of reach)
All this would have me nowadays make a square, easy to reach overflowbox which could be filled with a large coarse foamblock which would a) block leaves and large debris to get into filter b) be easily cleanable/exchangable and c) not be a hazard to fish and even young fish/shrimplets. Glueing the overflow box to the outside would be nicer to the tank, less obtrusive, but could also be done inside the tank.
In my situation the wholde in the side of the tank led to another small glued box to the outside of the tank from wich two pipes (one over the other) led to two clear pvc square 15x15 cm tubes. Both these pipes (app 130 and 150 cm high) where filled with bioballs and stood in the sump . So the water from the tank ran onto drippplates on top of the bioballs. i added some course foamblocks on top of these the be able to clean leaves and large debris before entering the bioballs. Basically this worked very well, except in a CO2 added tank this drives ALL the CO2 out of the water. ofcourse you get very well airated water in the sump which is good.
I removed these pipes because going high tech i couldn't keep enough CO2 in the tank this way. I may add a small pump and get some water through a trickle filter to add O2 to the water. That filter could even be above the tank and let gravity feed it to the tank.
The old sump was filled with pieces of lava and filterfoamblocks, and a compartiment with Siporax, lots of media. Going planted i removed most of it.Now i only use 2/3 foamblocks and a bag of siporax in it, being able to clean it easily is important. I shut off the pump, lett it drain so there isnt flow and siphon the compartiments clean.
If you make a sump it's always wise to make a way to keep the sump circulating on its own, independent from the tank. Keeping flow in there is needed for instance if you add medications to the tank and don't want them in your sump.
From the last compartiment of the sump a big pump (3000 lit/hour) pumps water back to the tank. There again i originally made a overflowcompartiment (again a small triangular space created by glueing a sheet of glass in a back-side corner.( Originally these corners and the back wall where hidden behind a DIY backwall, that came out after a accident where a piece broke off)In that corner i have the water coming in through a pvcpipe. When i started adding CO2 i added a diffusor like pipe to help in diffusing the CO2.
I am still contemplating some form of plastic sheets to get the overflowboxes out of view, so i don't see the stuff in there anymore.
So 1) easy reachable and cleanable overflow box, 2) easy reachable and cleanable sump are what i would advise.
I really want to try out the shallow & wide low tech tank thingee with a wet/dry trickle filter placed within a sump below the tank. 
That thing doesn't look like it's affordable to garden variety old me
. I was thinking of giving the job to a professional.