if you have an SUV use 10w30 if small vehicle 5w30 i would also recommend using fully synthetic at all times.
5w30
On the 2008, the manual says 5W30. However, many Lexus dealers use 5W20. I assume this is to try and improve gas mileage slightly.
Lexus uses Toyota oil filters for their vehicles, so yes, you can use Toyota oil filters for your Lexus.
The recommended oil type for a 2004 Lexus GS 300 is 10 W 30. The oil capacity for the car is approximately 5.7 quarts.
5w30
5w30
5W-30 Synthetic Oil.
Use exactly what is recommended by Lexus as listed in your owners manual.
Synthetic 0W20
Many models of Lexus. Best I can suggest is to see what the manufacturer recommends in the cars handbook.
I use 10/30w full synthetic from Castrol. Visit clublexus.com and you'll see many a discussion on the topic!
Vegetable.