Info on building a new hood

[Bruce]

I would like to build a new hood.
My tank is a 155 gal bow front.

I currently have a Hamilton Light with 3 175 watt metal halide with a 20k,
10 k and a 6.5 k metal halide. Also in the hood are 6 55 w PC 3 beinging
true atinic and the rest are white (I have forgotten the color)

This covers half of my tank from front to back. It is about 10 inches tall
and about 10 inched deep. Length is 6 foot.

I want to build a new hood to cover the front portion and want to add more
lights.

I want this to be a low profile hood.

I plan on having (in order for WATER up:

Clear Acrylic
bulbs (thinking about 3 90 watt power quads.Not sure what color yet... any
recommendations?)
reflector
1/2" styro foam (or 1/4" plywood - which would be best?)
acrylic (black)

Here are my questions...
How thick should the acrylic for the bottom be?
How thick should the top acrylic be?
What distance from the bulb to the bottom be?
What distance from the bulb to the reflector, and then the reflector to the
acrylic?
Should I have a fan? Should this be strictly controlled by thermostat?
I plan on having a mecrury switch to control the lights when they are
lifted. Is this a bad idea? I am thinking about enclosing this in some epoxy
so that if it breaks, it will not get into the tank.

Thanks!
Bruce