Good seeing your still here
Your tanks overflow will determined what size pump you can use as main flow. Also system turn over rate is based on flow from DT back to DT with power heads not counting. Power heads move water BUT don't change waters micro structure like flowing thru a filter does. Flowing thru a open top filter adds oxygen, changes water temperature, cleans, and adds micro fauna. It also forces lower warmer DT water to surface for removal since incoming water is cooler than lower DT water. We are talking micro scale stuff we can not see but corals and fish can feel.