Mine wasnt a complicated set up, they were bare tanks for breeding angels and growing on young discus
I literally had 4 tanks in a square on stands and in the middle on the floor, a 5th tank.
All four tanks had two holes drilles, one hole was just a hole and pipe dropping down into the sump (an overflow, as long as there is water going into the tank... water overflows back out the other hole..) and i made strainers so fish didnt go down! Just used pond hose as the pipework as it wasnt on show but you can use solid pipe.
I had a pond pump in the bottom tank with a hosetail and a few inches of hose and I used a 3 way splitter and a T piece to split the return pipe from the pump to cover the four tanks... the pump size will depend on the volume of water...
It was so basic a settup, pump pumps the water to 4 tanks where it overflows down the other pipe back down to the pump and it cycles round. The sump itself had lots of biomedia in it and the return pipes went in behind a sheet of sponge before going to the pump to be returned.