Help with gph in sump?

Hello im new to reef tanks so i need a little help in deciding how much gph to go threw my 20 gallon long sump. The sump well have three compartments skimmer, refugium and return pump. Basically im trying to understand if the return gph would depend on display tank size or protein skimmer specs. I already bought a reef octopus 150 sss and i plan to buy the return pump soon but i cant decide on Eheim 1262 or Eheim 1260 I have 5' of head loss for the return? The display tank is a aqueon 90 gallon reef ready with internal megaflow box which i believe is rated for 660 gph. Any help would be appreciated!