The sump itself is different depending on your needs. I used a 20 gallon long tank for my 75 gallon, I had 2 connected in my 210 gallon. My current has one area where I keep the skimmer and can put a reactor if I need it, this is where the drain goes. It then flows into a refugium area where I have live rock and algae, then it flows through the bubble trap into the return pump area where I have the return and my auto top off system.
Using a 5 gallon tank you may just have enough room to divide it once or you may decide not to divide it. It really does depend on your needs.
Of course you will need a hang on the back overflow to get the water down there and a return line to get it back up.
I kept a 29 gallon bio cube for a number of years I used the back area in the same way one uses a sump.