I think the plan is pretty solid. I do recommend that you add the zebrasoma tangs concurrently. However, they may not allow the powder blue tang addition. Kole can also be pretty aggressive and may not allow the PBT either. He's likely to leave the naso alone, and likely to leave 7 zebrasoma alone.
Your idea with the Naso isn't a bad one, but IME Naso CAN become territorial in small groups of tangs or if theyr'e an only tang, and with two spines and the large size, they can become dangerous. In a group, Naso are almost always very docile. But either idea is not a poor one.