I'm just running a basic glass 3ft (160L-ish) tank so it sits on top - I don't use the brackets that came with it, I just put a small piece of wood to give distance between the glass / lights to avoid overheating.
I did use that light by itself for a good month , with no visible problems on plants but growth was slow (Except cabomba, but that stuff will grow in hell.) But then again, I only had amazon swords, cabomba and java fern.
If you're looking to go minimalist with planting, you shouldn't need much light at all - perhaps even less than 1WPG.
But this is wholly dependant on what plants you wish to have.
What is the height on your tank ?