a: leather transforms the feel of any car's interior IMO
b: really enhances the front end, and look of the car at night; but you can always swap out for whiter halogen bulbs if you don't get them
c: you can probably do without these, certainly the rear view camera (if you already have PDC rear). I think PDC rear comes as standard anyway, so with a little care (with the front) you should be okay! Could help save you from some bumps etc. though so could save you some money/stress at some point, which is why I've put it above "d"
d: a great sounding system, but would be last on my personal list when compared to the above, and if you get the Hi-Fi system as standard (I think people in the US do), even less so