Maybe I'm dense or missing something here, but I strongly doubt that your 'live' rock has any nitrifying bacteria at all. It sounds like it was stored dry, which makes it plain old rock, just soak/rinse it in freswater before you use it, mostly to get the dust off!
Point A - A couple islands and maybe a ledge of rock is all you need for a shark tank, swimming room is premium, especially so in a 90g.
Point B - It doesn't matter AT ALL how much LR you put in that tank, using it as a filtration method for sharks is frivilous, and secondary at best. It will only be decorative.
Point C - PC lighting is only for your pleasure, it will not bring out any extra life from the rock except algae. And believe me, there will be algae. The same spectrums can be achieved just fine with NO flourescents, extra wattage will probably be a waste (imo).
Point D - 90g will suffice for a short time, but even the smallest more sedentary sharks like the bamboo will need at least 100g eventually (re: 5 foot tank). And most species will need a 180 and up.
Point E - Priorities. Spend that PC lighting money on a top-notch skimmer and wet/dry filter, and make sure that they will handle a larger tank than the one you have, because you'll be needing a larger one sooner or later. Buy a book like 'Aquarium Sharks and Rays' before you dive in headfirst.
Fwiw,
bb