Just a couple of observations. In the pic of the back of the tank the emergency pipe looks lower than your open channel. And all look kinda high, slight chance of overflowing the overflow box. May just be a dry fit that is shown in the pic.
A Mag 24 seems big for a return pump for only a estimated 145g system. Most returns are preferred to be 3-4x system volume. Depends mainly on skimmer requirements ie mine requires 1000gph. But I don't know you return plumbing head loss.