Would it be a really bad idea to gut the standard fixtures that come with tanks and retro fit them with one of these kits? I worry about the heat, but I've never owned a t-5 fixture.
It does not really matter which type of fixture you hang. What does matter is that you mount it securely.
I hung this one mainly to reduce light intensity because the bulb is a T5HO. You would most likely not need to hang a stock hood because they are T8s, which have a much lower light output.
The fixture barely gets warm. A hanging fixture would be much better at temperature reduction than one directly on top of the tank.
The two wood strips could be replaced with a board spanning both brackets, which would give you a shelf. I'm always looking for ways to make more storage space.
It's always nice to have more storage but we like the bare look. Plus, I didn't go heavy duty on the anchors because the whole setup couldn't weigh more than a few pounds.