If the dimentions could be cahnged I woudl make it a little shorter in height. At 26" you will need probably 400W MH
lights to properly light the tank. Thats a ton of bulbs also. As best I can tell you would need at least 8 MH
bulbs. If you made them 20K then you would not need any more light unless it was just personal preference. If you did 10K bulbs then you should supplment with VHO
With two closed loops I personally would shoot for something like 700-900GPH each. Have them run thru a sqwd or something else that would divert the flow over multiple outlets. A tank thats 5' from front to back and 8' from side to side will need a fair amount of total flow.
A 650-700 gal
tank would benifit from a 100+ gal
sump and a refuge in the neighborhood of 75-90 gal
. Size the prop tank to what ever size you want. If your proping tons of corals you sould probably go with multple prop tanks to keep the different species from going to chemical warefare with eachother.
You wont need a humidifyer thats for sure. YOu will need to vent the evaporation and humidity from the tanks outside else suffer from mosture damage.