First things first... (You KNOW I have to say something!
Take my comments lightly, I can easily seem like a know-it-all!)
Personally, I would try to get away from those HOT bulbs. They have a greater heat output per lumen then a fluorescent bulb, and cost five times as much to run. 150W bulb = 2780 lumens = 18.5 lumens per watt. A fluorescent fish-tank plant/aqua full spectrum light, "Life Glo", made by, "Hagen" (15W T-8 18in. bulb = 1000 lumens = 66.6 lumens per watt), and has a more natural noon sun spectrum. Translation, right now you have a fancy EZ-Bake oven, half full with water, that will be 1/4 full of water in about a week.
Since you want Terra and Aqua, I would use a 6700K (Full noon spectrum) tube in the back for the terra, and a 10000K (Standard underwater growing spectrum) lamp in the front for the aqua. Resting on a full glass top, that you can crack open to reduce heat and humidity. For size, I would recommend the 24inch tubes rated at 20Watts. The standard watts per gallon formula will not apply here, because of the sheltered water, and distance from the bulb. This should be enough to keep you growing, and not farming...
Secondly, I would move the heater and filter/diffuser directly behind the island that you have. This will help hide it a little. You can further hide it by using creative rock and plant placement. Just don't lean any stones against the heater, that may stress the glass and cause it to crack. Ultimately you may be better with a mini heater, since this is half full, and will have heat coming from the land. (Composting generates heat.)
I am also curious about the wood holding up the island... Will that rot, sending your island sinking to the bottom?
Otherwise, it looks great. A real novel idea, with the island setup. The mirror thing sounds great also. You can see what a mirror can do at http://www.plantedtank.net/forum/viewtopic.php?t=2518
she has a link to her photos. She didn't just add a mirror, she replaced her whole back glass with a mirror!