There are many personal preferences. Do you want a refugium section, or not? That is probably the main question...
My 20 long sump has a drain section with some egg crate and it forces the water under (so I can add rock, carbon, etc whatever I want really) followed by a middle section with a protein skimmer, heaters, and media reactor, followed by the last section that comes after a bubble trap and that is the return pump section.
You can combine sections 1 and 2, or use the middle section for a refugium, or do something entirely different. Just wanted to share what I did...