Awesome pics of the tank filling! The test fill is one of the most nerve wracking parts.
As for the water change cost comment - large scale tanks like these rely a lot more on natural process and don't get the same level of water change that most smaller (meaning 1,000 gallon or less) systems would get. Just a lot of sandfilter backwashing.
And decor actually goes in easier once there is water in the tank. Filling tends to move stuff around alot...even heavy rocks. But besides, doing aquascaping from inside is more fun once it's full and you have to wear dive gear!!!