Probably just add a little of my own experience from my own 2009 RX:
3. Lexus extended warranty is definitely negotiable, you can negotiate it as part of buying the car now or you can call around different dealers and buy it anytime up to the end of the 4 year manufacturer's warranty which I am assuming should be soon like mine. Don't forget to negotiate on Lexus roadside assistance as well, it is basically re-badged NRMA but I got it for cheaper than if I bought it from NRMA.
5. I just had my 75k km service done today for around $800 so having it thrown in is a good thing. I was quoted by Lexus to change brake pads last service for $900, I went to my own mechanic and asked for genuine Lexus brake pads and I was charged $500 parts & labour.
9. I assume you mean side steps, I quoted with Lexus for genuine ones for $1000 installed but ended up installing an aftermarket for $400 including installation in Sydney bought from Ebay, it is from China but surprisingly sturdy and works quite well.
You can't go wrong with an RX, Lexus cars are reliable, comfortable and fairly good to drive. All the best with the purchase.