Your stocking sounds good to me, especially if you have an oversized skimmer like you mentioned. The naso for sure, and possibly the hippo tang will outgrow your tank but that'll give you an excuse to upgrade. I think the norm is 6' wide tank minimum since naso tangs are such active swimmers. A cube setup is nice for now but once they get bigger, they'll need that 6' width to stretch their fins a bit.
I have a 125g and I have resisted a naso for 3 years now. Enter the new 215g that's coming soon...
Tank looks great. Always a big fan of cube tanks as I came from a nanocube.