Sure, that's plenty of space for 6-8 plants. Figure 1 square foot per plant. You have 14 square feet. Even if you give each plant two square feet, you'd have room for 7 plants. The problem is, you don't really have enough light for 14 square feet. For that much space, you'd be better off with a 600 watt light, or even a 1,000 watt light. 400 is good for about a 3' x 3' area, but the edges of that area will not be getting nearly as much light as the center. Light decreases proportionally to the square of the distance. So, double the distance, one fourth the light.

Maybe you could section off half the area, and create two 3.5' x 2' areas, and use the 400 watt light and the CFLs in one such area, and try 4 or 6 plants. Then later add another 400 watt light for the other area. Or dismantle the divider and just get a 1k light.