They aren't too difficult but what you have in the tank is determined by them. No Nems or other stinging/aggressive corals, no aggressive fish, no clams. Most softies are fine and you can't have super strong flow. There's a lot of good info in the seahorse/pipefish thread.
Wow. I am in the exact situation. I bought a waterbox 100.3. I have a 4 year 20 gallon established tank. I want to add my established live rock and 20 gallons of water from the established tank, then add some new (marcorock) and 80 gallons of fresh saltwater. I was concerned about moving over my corals and fish to the 100 gallon system without doing a complete cycle. I am so glad I came across your post. Thank you and your tank is looking good.
Up and Running. I did not have the luxury of time to left this tank sit and cycle since my 60 gallon marineland was about to bust a seam. Tank was set up with a combo of rock from my old system and new rock and a combo of new water and old tank water. The sea horse and clown fish seem very happy so far in their new home =)
There is no Fuge section in the Waterbox Sump so I got a baffle from OctoAquatics
