Refugium: It depends what kind of fish you want to keep in the tank. Certain fish are very difficult to feed like mandarin dragonetes and require live copepods. To produce enough live copepods in a tank you need a very large refugium. So for a select few species of fish like seahorses, with difficult feeding requirements, yes a refugium is usually needed. but there are numerous exceptions like buying copepods every week, you would have to spend about 100$ a month on copepods for a single smallish fish. Which usually deterrs people. Or you can try training the fish to eat prepared foods. This training process is like being through hell and back, twice. You will probably end up killing several fish before successfully training them. And by then it might already be too late.
A carbon reactor, it would depend. If you are using rodi water in your tank and you dont have serious phosphate problems, no. If you are using plain dechlorinated tap water then yes, because tap water contains many toxic chemicals like chlorine, tds, and sky high hard water. City water even more so. Well water, not so much. It depends how heavily your water treatment facility doses chemicals. but i would definitely try at all costs to avoid using tap water. Rodi means reverse osmosis, deionization. This process basically converts polluted water back to a purified form. You can also d this at home.