Some Rockwool growers should chime in here. Seems like your within the parameters though.

2.5 x4 x4 on top of a 6x6x6 will work fine, I prefer 2.5x4x4 on top of a uni-slab. Rookwool can be used very simply or can be used very technically meaning with inputs/meters etc. when I started out with Rockwool I knew shit, but now I run it far far different then I did, and I can tell you Rookwool is only going to put out based on how its run . if your just going to run it simply its probably not going to produce any better or as well as sunshine or coco. its inert it requires some dialing in of nutrients to work best, and its easier to have root issues with it as opposed to soil or coco . My first grow with Rookwoo was really no better then soil, but I seen its potential and started playing with, Rookwool is all about maintaining, PH running proper ec, number and amount of shot sizes and duration through P1 P2 and P3 a lot of that will depend on if your looking for quality or mass. so stacking the ec in the medium is very important, how you do it, how fast you do it and how much. That EC will all depend on you lighting and environment and is not going to be the same as coco, runoff will control PH and EC, so the idea is stack P1 more short shots off nutes, P2 maintain, with runoff only starting at the end of P2 and a P3 if needed. I do not concern myself with dry backs , maintain pressure PH and EC is far more important , I start out with 1.1-1.2 ec right out of the cloner, depending on the phase and where I'm at in the grow I'll stack to 3 ec no issue . whether you run generative or vegetative will make a difference in the above. it will for mass and quality as well. depending on light scheduled 18 or 12 I feed 25+ times a day, so an automated setup and good timer comes in handy.