I have a 120 as well. You're going to want to get a 40 breeder to use as the sump. You'll put your skimmer down there as well as probably make a fuge and have a place for your return pump and heaters.
You'll need powerheads. I use two tunze 6105s but you could get buy with something cheaper depending on your budget.
You're going to need some kind of lighting. LEDs is all the rage right now and you could research it if you want to go that route. DIY, ai sol, and radions are the big ones. I went with metal halides and use radiums driven on an M80 magnetic ballast.
I like the reef octopus skimmers for the best bang for your buck. A SRO 2000 would probably suit your needs depending on bio load.
Maybe a few reactors for carbon and GFO. You'll need heaters, I like eheim jager heaters.
an RO/DI is highly recommended. Bulk reef supply and buckeye field supply are highly recommended. 75 GPD should be adequate.
And last but certainly not least, don't forget to set up a 20-30 gallon quarantine tank for all new inhabitants.
Good luck :thumbsup: