When I first started out I used a couple of T-5 fixtures ( 4 foot X 6 bulb ) to veg. and then flower. After several grows I switched over to 600 watt Hps and have never looked back. The HPS has more penetrating power than does the T-5's and I think the HPS produces much tighter bud formation. The T-5s really shine when used to veg your plants. As far as heat is concerned the T-5s generate heat also, and with the amount of bulbs (32) you are thinking of using you will need some sort of ventilation to cool everything down.
I would suggest that for the size space you have to work with 2 600 watt HPS systems would work better. You would still have about 5600 lumens per square foot.