I think you should just sell me that tank because your lights won't work too well on it, and mine will!
I heard about the deal you got on that.
Anyway, I think you're better off with halides for this setup. A couple of pendants would work well so you could space them evenly. I would suggest 2x250w either DE on HQI ballasts or SE on electronic ballasts, then be careful to pick bulbs with decent output. I would suggest Phoenix bulbs either DE or SE depending which setup you decide on, or Aquaconnect bulbs if you're feeling rich.
Then use big reflectors for good light spread like the full size Lumenarc, Lumenmax, or Lumenbrite. If you plan on going with SPS in the future I would suggest 400w just because of the spread issue.
However, with mostly LPS and softies I think you should just try your 8x54w T5 fixture for now, you may find that is enough light. Just position it in the middle. Or I think you would be fine with two 4x54w T5 fixtures, one on each side of the overflow.