OK, so you are going sump, you are going to need high quality lighting, and skimmer. In your sump you probably want to set up a refugium.
You are going to need rock. Live rock, or dry rock, or DIY live rock. But you need it in the tank for biological filtration.
55 Gallon, DIY Live Rock, 2 Taotronics 130w LEDs, CPR HOB skimmer and refugium, 525 GPH SunSun 5-stage Canister with UV Sterilizer using Chemi-pure Elite, and Two Fishes GFO reactor and 3 800 GPH powerheads. <><