Hi Ti-mo:
Welcome to the club.
Regarding your questions above. I believe the Mark Levinson Stereo is pretty nice and classical music sounds quite well through the speakers. They may not sound the same as the Bose in the Audis but there is plenty of clarity. Bach and Mozart sounds okay, and Tchaikovsky sounds really good. American Jazz sounds really good on the ML.
Regarding the IS-F wheels, I generally don't recommend using 20" wheels for snow driving; too much contact, but you are limited because of the Big Brake Package, which is the reason why I own a Subaru. I would recommend something cheap during winter. ISS Forged Wheels look very good on this car.
Regarding the suspension setup between the 08s and 12s, couldn't really say since i haven't driven the new ones yet. Unlike the M3s the shocks do not adjust so it will be a harsh ride during Normal and Sport modes. I though they did too, but only the throttle response time and the gears shifting are the only noticeable differences.
The coloured jeans issue, haven't really heard anything about that before, but I don't have a tan interior. I love the leather, soft, but I am not a particular fan of the tight front seats. They hold you very well but since the car is so small it's a bit tight for me. I would be cautious with the white; keeping it clean would be my biggest challenge.
As far as the Lexus warranty it's pretty well suited for a semi-race car with a slightly-light-rear-end. The limited slip will throttle down the engine whenever it's needed in normal mode and sometime in sport-mode. I have noticed extensive use of the sport-mode and the paddles can smell up the interior with that clutch burning smell. Lexus does not recommend modifying the car in any way or form unless you're using F-Sport products. I haven;t really challenged this during the warranty period, but you could opt for an intake and exhaust to give it a louder sound. I would check with the dealer before you try that out.
Now regarding the track testing, I am curious to what time you'd get :). I haven't tracked mine yet, but someday I might, and I would have to switch to a larger width wheel and tire on the rear end.
Either way, I think you've bought a fabolous car. it's a lot of fun and because I am one of the few in the Washington DC area diving an IS-F I get a lot of challengers. Either way, you will enjoy the car, and let us know what the car does on the track.