I don't know about this pipe air idea. Will it give same amount of air from every holes? You need some wind for the plants.

300w looks not enough for 16 sq foot. It makes approximately 1500lm per sq foot. You need to double it to get some good results.
Use T5 HO or PL-L and make it from four sides instead of 30w floros.
Or even use all T5HO or PL-L, don't use 250w single cfl. For T5 you can use 39W maximum and you need many. PL-L has advantage, higher wattage with short length. You can use 6x80w PL-L. This makes 2250lm per sq foot, this is enough. Use eight, 3000lm per sq foot, you're good.

PC fans are close to one side. Why is that?