Canisters are a pain to clean and trap detritus. Which will cause nitrates as well. A skimmer will pull stuff out without trapping material like mechanical filter pads do before it causes a problem for the tank. Turbo floaters are good skimmers, make sure you use a needle wheel impeller on the recirc pump to get the best foam. I have a client with a turbo floater and it pulls some nasty stuff out week after week.
Refugium will help you to reduce nitrates if you grow some algae in it (chaetomorph), nitrate is used by the algae as nutrients.
Benefits of a sump are increase your total water volume, hide all your nasty filter junk (heaters, uv, skimmer etc.) and with the overflow crashing down it helps aerate the tank.