High Pressure Sodium and Metal Hallide are BY FAR better than Halogens. They also dont glare on the water like Halogens do. But they get expensive in a hurry. Its been said that HPS is best for murky water, MH for clear. That could just be speculation though, Im not familiar with MH.

I got 6 150 watt HPS lights from E-conolight.com They are the least expensive fixtures I could find. They are really sturdy lights though. They run around 40 dollars per fixture, but you can plan on another $8-10 per fixturefor a capacitor to wire in. If you have the time for a wiring project, these fixtures can save you alot of money versuses the 100 dollar fixtures of other companies.

The 500 watt Halogen bulb puts out up to 10,000 lumens.
The 150 watt HPS bulb puts out up to 15,000 lumens.
The 400 watt HPS bulb puts out up to 50,000 lumens.

How many lights is based on just how bright you want things. If i was running 400 HPS, I would go with three. I went with 6 150 HPS instead because of prices. If you run 500 Halogens, just run as many as you can on your genny, they aren't very efficient.

How high off the water is based on your boat. Put em on the gunnel if you dont have an elevated deck. If you have an elevated deck, hang em underneath it. Angle them based on what gives you the best water coverage. My lights will end up being around 2-3 feet off the water.