Agreed.
Also look into the recommended water level for your protein skimmer. Most people set it on a pvc stand to get it at that water level. If your sump is too high then you'll have to raise your protein skimmer even more which you may not be able to do if your stand doesn't have room for it.
A typical layout (even though there's many ways to do it) is to have the skimmer first, bubble trap, refugium then return compartment. Size the skimmer and return compartments according to your equipment size and the rest of it becomes your refugium. I'd go with a 30 long if you have room for it in your stand so you can have a bigger refugium.