I did get a price from Chris last year. Over £300 each and I'm not sure if that is with centre caps (which are £33 each).
There are 3 on ebay at the moment (no centre caps) - I have 6 of them so I can let one go but I haven't tested if any of those are buckled.
Not heard of problems with the series II OZ sport wheels but you never know. They are expensive - much more than the series I wheels.
Somebody in LOC had a series I with series II wheels. Never saw a picture - I think they have sold the car now.
I wouldn't. EGR can reduce engine power but Toyota program the ECU to compensate for it and by disabling it you may get too high engine temps. or get knocking which will be detected by the knock sensors and retard ignition timing (which will reduce power anyway).
This explains more:
http://www.autoshop101.com/forms/h61.pdf
Lexus haven't release fuel consumpsion figures. The 600 miles won't be on the combined fuel figure.
The engine runs all the time unless you come to a stop.
The 400h is not just about economy. It's also being sold as a higher performance RX.
Not really sure what you are asking. An engine swap? If so then you would need ECU, radiator, gearbox etc as well as the engine.
If you are thinking of selling you 300 and getting a 430 then I would say yes if you can afford it.