What does RBH bring to you that the others don't? I haven't had the chance to listen to them, so I have no comparison point.
I will say, though that 5 full range towers, if you can do that, would be a monster bed layer. Or at least two full range at your mains, and the slightly lesser siblings at center and Surround... (just an example to illustrate (not full range, though): Monitor Audio Silver 500 as L/R, MA Silver 300 as Center/Surrounds)... then you have a little more leeway for sub placement. But if you can get full range at your mains, you can go Geddes style with your subs, and pick the 3 best places around your room to supplement the mains.
At 3000'3, i think sealed subs could be a consideration. I know its a bit of a heresy, but you will have cabin gain in that room, and I think it can work in your favor. Just a suggestion to experiment, not an earnest recommendation.
Regardless, you've got a lot to work with! Completely blank slate.
Look forward to hearing more about this!