Whats the best wattage/power bulb to use?
Generally, the most that you can afford and/or deal with. The more powerful the light, the faster your nitrate, phosphate, and nuisance algae will be reduced, and the lower they will stay. The bare minimum for any setup is a 23W CFL Floodlight, 2700K. A maximum might be 65 watt bulbs, but you can have multiple bulbs, of course.