How many lamps you will need will depend on the spread created by the reflector of the clamp lamps you buy, and the dimensions of the tank. I'm going to assume it a 40B so it's 36" long. I was playing around with those clamp on shop lights and three seemed to give me full coverage. So I would say start with three and if you feel like there are gaps in the coverage add another later on. As far as the bulbs are concerned they are a good spectrum, but for a shallow tank like a 40B probably overkill especially if you aren't doing pressurized CO2. I would start with 6500K daylight cfl's at Lowe's(or someplace similar) that are 75W equivalents instead of the 120W equivalent ones you linked. If you find they aren't strong enough you can always use them in you're lights around the house if you decide to upgrade the ones on the tank so it's not a loss. If you buy the ones you linked and need to use something smaller you probably don't have many places to use a 120W equivalent bulb. Just my .02 cents
"Not my circus, not my monkeys"