a 7 inch screen fits in the satnav area well
the bose doesn't have an aux input - it's possible to modifiy it so that the tape input is used as an aux one but this involves cutting some traces and soldering a few wires onto the circuit board. my350z.com has a guide on this. or just replace the bose head unit (you will need a PAC adapater if replacing head unit and keeping the bose amp)
a few people have installed screens (for car PCs) in the space - search under my name or under Zedrush in the ICE section.