See my reply in NRK forum about sumps. There are so many ways to run a reef tank.
You need the essentials in most tanks.
Proper Lighting, for the type of corals you plan to keep.
If you plan to keep clams and stony corals, your lighting needs would be different then someone attempting too keep just softies and shrooms for instance. Same goes for calcium/alk maintenance, in tank water movement, and over all water quality.
It may be wise to grab a basic reef keeping book.
If you know what type of corals you plan to keep, let me know. Otherwise if you are just starting out a nice soft coral reef can be very rewarding. It can be maintained a bit easier as well.
I would recommend a beginner starting with soft corals to invest in a quality protein skimmer, quality lighting for their tank (T5, VHO, or in your case of a corner tank a single 175/250 MH with a pheonix 14k bulb would work), a reactor to run carbon or GFO (bulk reef supply, or two little fishes style), a
refractometer, and some way to increase in tank circulation. Maxi jet now sells a pro version that include a prop to allow a nice wide flow pattern.
Substrate, if you decided to have one, I would recommend something between, fine oolite sand and special reef grade, nothing larger.
Also some quality live rock. Again let me know if you have specific questions.
