Lesterkiwi

As to the original question of maintenance. I've worked on Lexus for over 11 years. I wouldnt worry about the timing belt untill 90 or 100k. When you do decide to change it make sure you get the water pump, idler and tensioners replaced as these are the parts that fail causing the belts to break. Also get your crank and cam seals done at the same time. If not they will eventually start leaking, and you will have to pay virtually the same labour as the replacing the belt.
I would recommend however, replacing the transmission fluid. Your car likely has a U140E transmission which is notorious for breaking. I would recommommend doing a drain and refill every 15k.
As far as oil changes, you can go 5k on regular oil with no problems. I used to work at the dealership and the sludge issues came from people going longer than the scheduled maintenance. Every ES and RX where the customers changed the oil at 5k were fine. Change the oil every 3k if it gives you added piece of mind.