Floro cabinet grow in week 5

[PhatJay]

i will have about 16 inches of grow hieght left for the last 6 weeks of flowering. is this going to be enough space?

Yes.

should i tie down the main stalk as well?

If your CFL bulbs were mounted in a reflector, having a main cola sticking up above the canopy means that the lights are quite far from the secondary buds and this will decrease your yield. Because you have bare bulbs and can hang them around the main cola nearer the top of the canopy, training the main cola is not critical, as your secondary buds should still be close to your bulbs.