5500k will work fine, they just might not be as efficient as 6500k. Also two bulbs will work, esp for now when there seedlings, but you won't see as much growth in the same time vs with more bulbs and your plants may stretch when they get bigger as they keep reaching for the main light.
Any proof to this? From what I've read, the 2700k bulbs don't help much with actually vegging but may help stem growth or are you talking more of a 5000K bulb mixed with a 6500k bulb?
I guess it would depend on the distance of the bulbs from the clones. They would work great if your plan is to place them 6-12 inches from your clones so you can cover much more surface area for more clones. The closer you put them the more they will make your plant sweat and dry out, thus...