You don't "have to"
buy a 72" light set up but if your going to have any success with corals of any kind, you will regret not going in that direction. Simpley because a light covers a certain area doesn't mean it's adequate to support light dependant animals. Intensity vs depth is moreso important. A 4x96w PC
light will extremely limit what you might be able to keep successfully.
As far as a FOWLR
set up, lighting is much less important. If the PC
was elevated a bit more above the tank, it would illuminate more area but light quality will be greatly reduced. It will support coralline at the very least.
I guess the best suggestion here is to ask yourself what do you want the tank to house and what your eventual goal for the tank will be. There's no reason why the tank cannot be set up in stages and more appropriate lighting added later if you decide to keep corals and your budget permits. As far as the rock is concerned, it needs no special light if used (in the beginning at least) soley for biological filtration. If that's the case, a simple NO
strip light will be sufficient.
Lighting is pretty pricey so I would be sure it's something you only do once if possible.