Hey mate, first of all the official colours are sunset orange, azure (blue) and white im not sure!
Most of the Z's are manuals, i have a manual and love it! Look out for stiff gears particularly 4-5-6 and also check for clicky rear axle, a common fault with the Z! (Can hear a click when moving off specially when from revese to first apparently - must have the window down though!
id personally get the GT pack as it comes with all the nice extras - heated seats, bose sound system, leather seats, cruise controll and handsfree button on the steering wheel!
If money is no object go for the facelift version, the first change to the z was in 06 with a 296bhp model over the standard 287 and the 07+ have 313bhp although the torque figures are different on each model and the pre 06 Z's have more torque stock than the newer models.
With the facelift versions you will get a slightly nicer interior and on the 06 a different bumper with 2 larger slats, bigger xenons and LED rear lights and some other small changes... i think the zorst note is louder on 06+ stock exhaust too
with the 07+ you what the 06 has plus a bluge in the bonnet and there is a light around the ignition i think.
Dont count out the import models as you can get some nice deals on them
Good luck
oh and sorry!