a refugium is a place to grow and have macroalgae - macroalgae converts nitrates to x. <-- i am sure someone will elaborate, but that is pretty much the basis of a refugium.
Filter sock is a mech filter that catches debris and clarifies water <-- must have IMO.
The more LR the better, more biological filtration.
Carbon, all i know is that absorbs nitrates and other bad things, you should also change it out once a month. Unless you buy seachem carbon then you can change it out every 3 months. Carbon is pretty complex - obviously i dont know much about it, i just know that it is good to have.
Hope this helps
Uv sterlizer requires its own pump w/ very little flow through it. A sterlizer kills parasites, algae, and also clarifies water.