Do you know the cost different between piecemeal and just doing the whole car? I'd be tempted to just do the whole thing. All those areas are good to protect you from rocks your own tires are throwing, but my daily has chips in the most random areas from other cars throwing stuff.
Plus, you'd avoid the possibility of seeing the edges of the film. I had a car that was done only in the "danger areas", and after years of sun and exposure, the edges started to lift. It looked terrible. I'm sure that was more of an issue since my car was parked outside a lot and your Z likely won't be, but it's something to think about.