Time and effort and it can be done fairly easily.
http://www.lexusownersclub.co.uk/forum/index.php?showtopic=48020&st=0&p=507902&fromsearch=1entry507902
You can fit the Sony Satnavs or Tomtom into the screen unit.
they go for whatever people will pay for them mate.
Ive bought them for less than £100 but also seen them go for £200 plus.
Plenty on ebay for the IS200, try also Altezza as the body is the same.
as for tuning specialists not many, though i use Silverline racing for my work and theyve been awesome
The unit can only be a replacement for a car thats already got the satnav you cant fit it to an IS that didnt have it,
the screen bit though people buy and fit their own screen or satnav unit into (ive made a few to sell myself).
1) if you can get one from a breakers for £100ish you can fit it yourself very easily, and yes they fit.
2) the tints are really quite light and only the back windows anyway.
The M45 is the same as the one they put on the Cooper "S" and as far as i remember used to be advertised as 1l to 2l engines, therefore on the limit with the 1GFE.
Personally people know the M62 works and i'd recommend using one but hey we never move forward playing it safe.
My Engine is from a Mkiii Supra, but its the 2.0L 1GGTE Turbo engine from the JDM only one.
Not sure if theirs any Turbo ones in Brum,
But Steve @ silverline racing did the engine conversion on mine. He's based at Cannock.