Good choice with the M35x. Here are the details per your post:1) Navi w/out Back-up Camera - NOPE. Technology Pkg. includes Navigation system, rearview camera & Bose sound system. Cannot get them a-la-carte. Just get everything!
2) Spoiler - If the M35x has the Aerodynamic Body Kit then Spoiler is standard. You can also get one with just spoiler. If it does not have one, the aftermarket will work just fine.
3) Sound System - While I'm no audiophile, IMHO this is one of the best sound systems comparing to Mark Levinson, Bang & Olufsen & other Bose systems. You can add an extra Bass tube in the trunk without too much aftermarket intrusion.
4) Winter wheels/tires - Not sure if you really need it since you are getting the AWD model.
http://www.tirerack.com or
http://www.discounttiredirect.com should give you a good idea on these.
5) Warranty - Absolutely, positively nothing other than the Infiniti Elite Protection Plan. Prices vary based on your current mileage and desired coverage. Courtney @ Infiniti of Scottsdale has the best prices anywhere for the IEPP. I paid approx $1300 for 3yr/48k coverage.