you didn't mention the wattage, this is a big factor. Anything is going to heat up. All ballasts get hot over time (hours). If money isn't an issue though go digital just because they create less noise and are lighter. As far as hoods go if you want something air coolable just go with cooltubes, easiest to cool, take up almost no space, and provide for the best airflow.
I designed a room for a friend once that was in a small closet, roughly 5ftx5ft that backed up to a bathroom. We put in two 600 watt and one 400 watt cooltube. We built a wooden box that we attached high on the wall and mounted all of the ballasts in the box. Air was pulled through the open 400 in the back corner and through the two 600's. Then the air flowed through the sealed wooden box holding the ballasts, through an air filter, and then out the back wall into the adjoining bathroom. Fresh air was able to come in around the closed closet door since light leaks were not an issue and this design created a room that stayed a constant 5 degrees above the rest of the house, house at 70, room at 75 with lights on, 70 with lights off.
