There are some excellent stickies with information regarding lighting. Look under the aquarium plants section of the forum. Regarding the light, more is not always better. I made that mistake! Too much light=too much algae. What type of light fixture/hood do you currently have or want? That will dictate your lighting options.
Cabomba requires high light and high nutrients. There are several varieties of Cabomba. I have the purple and don't personally recommend it, it takes really high light. Mine does well floating right under my T5HO bulb, but gets spindly looking when planted in the tank. Your best bet is the Cabomba caroliniana
, the green cabomba, which takes a little less light. I have grown that successfully in the past. Sometimes it grows, sometimes it won't. There are other stem plants that, for me, also seem to do well floating: Rotalia, Egeria densa (Elodea), etc.