What's the grow area? I know I could grow 30 plants in a 3 x 3 area with a whole lot less than 1800 watts of T5s. But the more room they have to spead out the more light you need.
More then adequate? That's 10 plants per light.That lighting is more than adequate for what you propose. Is your attic well vented? 1800W of lighting could create major heat issues. I struggled with temps in an attic grow, with only a single 600.