The choices are limited simply because most of them at dealers right now will be demo vehicles. These are usually in certain colour combos e.g. white/red, red/black, red/tan, yellow/black
Be careful with the 21" wheels. They're chrome and I believe they're quite expensive to get sorted out if you hit a kerb. I would also be aware that Lexus don't tend to use a lot of chrome wheels in the UK so would be concerned about the long term durability, especially pitting etc
You also need to be aware that whilst Sonic Red is a great colour, any dings/prangs and you'll have an expensive bill on your hands. The colour is very difficult to match and I know of 2 vehicles which have been written off as a result of the cost of colour matching a bumper!
All LCs in the UK have Run-flat tyres. There is more choice with the 20" wheels in terms of tyres. Currently, for the 21", there are only pirelli and Bridgestone widely available. Both sizes are roughly around £1000-1500 for 4 tyres
You have to be aware that the Nissan GTR is very stiffly sprung to begin with. The LC is designed with run flats in mind and the suspension has been tuned to accommodate this. It is firm, but nowhere near as hard as a GTR.
Remember that these cars are not cheap to run. Cheaper than some rivals yes, but servicing needs doing 1 year/10k miles at nearly £400 or £600. Later services are more expensive. I also doubt you would get anything significant in terms of discounts on these.
Depreciation is yet to be seen but in 1 year, there are some available currently which have lost about £16k.
The LC always reminds me of an Aston Martin when driven.
Additionally -
red with black
https://www.autotrader.co.uk/classified/advert/201805196672385?model=LC 500&advertising-location=at_cars&onesearchad=Used&onesearchad=Nearly New&onesearchad=New&sort=price-asc&make=LEXUS&postcode=wf177rs&radius=1500&page=1