Some of my thoughts...
That looks like a very large, long tank (you didn't say how big). I would only ditch one light and go with three 150W metal halide pendants. One in the center and one on each end. Plants tend to be adaptable to multiple color temperatures, but I would try to go with 5500 or 6500 K bulbs if at all possible. Setting up the three pendants would require modifying the ceiling fixtures though.
Set the heaters up like the lights. One in the center and one on each end. Two is probably enough however... in which case one left center and one right center. They will all keep turning each other off when they are so close together like that.
The filter intake should be on one side of the tank and the output (spray bar) should be on the opposite side. It looks like you have a HOB (hang on back) filter on there as well.. that's good, put it tank center.
Read up on water chemistry. Some of my personal comments:
CO2 - Pressurized system, stays on constantly. Consists of CO2 tank, pressure regulator, and "reactor" plumbed inline between the cannister filter and spray bar. Most people use a needle valve and bubble counter to "see" how much CO2 is going in; I do one better and use a mass flow controller which keeps CO2 at the constant rate I set at all times with no fluctations.
Calcium & Magnesium - Does not need to be "dosed," it affects the water's hardness. It should be added in a 3:1 or 4:1 Calcium:Magnesium ratio at each water change to achieve the desired hardness.
Nitrates, phosphates, and traces can be dosed twice per week. You can increase nitrates by simply adding more fish, and the phosphates will also increase since you'll be adding more food.
I dose iron daily.. but I use Flourish Iron which is a weak complex that breaks down quickly.