Thats a great choice made buddy.
talking about the accessories you mentioned-
Rear deck lid spoiler - I am not a fan of spoilers, but a Lip spoiler looks great on the chevy. Cost - 6K without paint.
Twin exhaust tailpipes - Would Void the warranty.
Turn indicator in external mirrors - Definitely get them.
Cost - 2800 ( Chevrolet authorized).
Xenon curve projector headlights with dynamic levelling and corner function - you can go for xenons and projectors , but i don't think corner and levelling function would be available.
Cost- 17K for A8 styled headlights
Automatic headlight system with light sensor- Can't be done.
White LED position lights - this is a cheap upgrade 150 for 2, 12 LED bulbs.
Automatic retractable headlight washers- Not possible
Warning lights on front and rear doors- Maybe done, not sure.
Corner function with front fog lights- Not possible.
Rear fog light- Not possible, But do upgrade your tail light to E class type LEDs.
Daytime running white LED headlights - 3800 for a pair
Tyre pressure monitoring - it can be done but i don't know the cost
Parking sensors and speaker at front- Those won't be required
Parking display on central infotainment system - Not possible on the stock system.
Audio player with touchscreen controls - 35-40K with GPS
Seat cover- Come on! you don't need seat covers for those nice leather seats!!
Leather steering cover- Already leather wrapped.
Retractable screens for rear windows and windscreen- 800 for a manual rear windscreen curtain. Can't say about the window ones.
Auto-tilt of external mirrors on reverse gear selection - Not possible
One-touch operation for windows with bounce-back system - Would void your warranty.
Automatic closing of windows and sunroof on exit - not possible
Automatically openable/foldable external mirrors on entry/exit - Not possible
Diffused footwell lighting - LED strips for both sides front( underneath dashboard) and rear around 4K.
Boarding spot lamps- i don't know what these are.
Reading lamps at the front and rear- can be done by chevy.
Illumination of luggage compartment with two boot lamps - there is enough light in there !
Rear mud flaps- 1400 for 4 mudflaps
Front glovebox with cooling- Can't be done.
Boot mat- Chevy would give you
Car cover- 1500- 2000 by chevy
Car perfume- Ambi pur
Foot mat - Get transparent or black ones over the carpet.
Air pump- very much needed . 1300 bucks.
Car inverter- store it in the centre armrest . Can't say about the cost, i got it from Dubai.
Illuminated scuff plates- 6K , please get them from your dealer only.
What colour are you buying?