i would argue(because i like to)that ro water is just as important in a fowlr depends on how you see it i mean if you want to avoid algae problems then id suggest it because your cleanup crew is limited in a fowlr....normally.... but in your case with clowns you can add anything you want in the way of inverts etc...but youll be on the coral train haha
and i personally prefer to get liverock from others tanks a little here from one and a little here from another adds diversity....lr in most stores is no different except there may be dieoff already depending on where it came from or how long its been sitting in their tanks so youd want to cure it no matter what just to be safe...where as rock from an established tank is already cured and you can control the amount of dieoff by the way you transport it.aot of times lr in a store comes from shut down tanks anyways lol
go for the biocube..... unless you can see yourself with a large tank......problems happen faster in small tanks larger systems are more stable but costly.....cheers