You definitely sound like you know what you're doing. The only thing I worry about your proposal would be the lighting to make sure it's enough. Since the tank is 18" high, I don't know if it'll be enough. I recently got an 18 inch cube tank myself and ended up getting this Kessil A150 led light. This isn't my tank but it's from my LFS and they've used it successfully on a number of their tanks (and reef ones as well but with a different variation kessil)
<- More pics there
I've only had my Kessil up for a week now and I'm not going co2 route (yet anyways) so I can't comment on how good the light is but it's the most expensive light I've bought so I think it'll do well. Also, as you can see from the picture, it's pretty clean if you go with a canister - just two tubes there. You could also do inline heater, and co2 reactor, making it even more streamlined... just my 2 cents though.