Biocubes are great b/c they have almost everything you need to start. There are a lot of modifications you can do later on if you want. They sell a biocube protein skimmer, but I wouldn't recommend getting it. It's just too small and gets full easily and isn't good from what I've read.
All you'd need besides the tank is:
-hydrometer or refractometer which is more accurate
-Test kits (API works, but Red Sea and Salifert are more accurate)
-powerhead (optional, but might want more flow. Koralia nanos are great)
-Sand (or not if you want to go bare bottom)
-Rock (you can do mostly base rock and some live rock to seed it. I personally did 100% base rock for my 70 gallon b/c of cost, but different pros and cons)
-heater (if it's not included)
-Salt (Red Sea Coral Pro salt, Reef crystals instant ocean, Kent Marine are a few great salts for reef tanks)
System or some place you can buy RO
water. Water source can cause problems or lead to your success. It's very important you start with great pure water. At last resort you can buy distilled water, but don't use tap water!
Hope I didn't forget something. Zoas and mushrooms are great beginner corals. Most LPS
like duncans are easy too. Along with the clowns and gobies, a purple firefish or a small wrasse would be awesome. Reefing is super addicting, but rewarding and fun. Good luck