WHat you're looking at in that sump build: 1) the skimmer ---removes amino acids: 2) a GFO reactor (removes phosphate). It will also contain the ATO (autotopoff float switch) and that will need an ATO reservoir to supply fresh water to keep the salinity steady. And the heater and return pump (about a Mag 9.5 (950 gph)) ---there's more gear, but once you have it going, it takes care of itself pretty well: refill the ATO reservoir, run weekly water tests, and feed the fish, which also feeds the corals. Stability is key to success, that and setting your salinity, alkalinity, etc properly in the first place, which you do with a good salt mix and a little hand-dosing and testing. Once you have it right, there are ways to hold it there for weeks on end, especially with stony corals.
Getting a reef-ready tank saves a lot of hassle: spendier, but easier. Skimmer, lights, and pump are the pricey items.
OTOH, I have a thread floating around here about managing a very basic marine tank with a couple of inexpensive Penguin filters---you'd need the ATO.