You have several options... but I would start with 3x250watt HQI ballasts (I like thePFOs, but Im sure there are other good M80s out there), with lumenarc DE stealths or pendants. Depending on how much room you have left over, then fill in the rest with T5 bulbs.... perhaps 4 rows of 80watt bulbs.
You dont need T5s BTW... you could just use pheonix bulbs or something similar (G-man 14,500Ks) depending on how much light you really need. prugs for instance, ran his 210g for a long time with nothing but EVC ballasts, PFO mini reflectors, and pheonix bulbs and did very well... considering the boost you will get from the HQI ballast over the e-ballast, and the better reflector you would have with the lumenarcDE... you could be set right there...
But the best tanks I see are halides with T5s... the halides provide the full daylight spectrum with 10,000Ks or Ushio type 14,000Ks, and the T5s provide all the blue and actinic. To me, the halide only option is a 'hey, your tank looks good' option, and the halide + T5 is the 'holy crap look at that!' option. It really brings out the colors in corals better than anything.
So you can go 3x250wattDE with 10,000K bulbs, then 4 rows of 80wattT5s... 2 bulbs as actinics and 2 as blue+. Thats a very sharp combo... top pick IME. The next best would be if you only wanted 2 rows of T5s... then use ushio 14,000Ks with 2x80watt T5s running blue+ bulbs for the T5s.
Here, I can even show you a pic from a friend's tank who runs 3x250wattDE Ushio 14,000Ks w/ 2 rows of blue+ T5s...
It looks sweet in person.
And here is a pic of a 120g tank that runs 2x250wattDE Ushio 10,000Ks with 4 rows of T5s... 2xblue+ and 2x actinic03... your 180 would be pretty much the same as this, just 50% more...
