Outdoor flood lamps are usually in the 65 - 75 watt range. Pool bulbs are 300 - 500 watt bulbs, usually heavy duty type (rated for more than 120 volts). They are also a specialty item and that usually means a higher price. I've seen pools with standard flood lamps in them, very poorly lit.

The gasket is all you need, just put a LIGHT coat of pool lubricant on it (just make it shiny) and tighten the clamp. With a new gasket it shouldn't leak.