No offense , but If you can afford a LS430 2002 with 16K miles, I'm sure you can afford the required gas for it. I have a 1990, that only burns premium, I had a 1980 Honda accord that only burned premium gas. Please, it is a crime to burn anything less than premium in that machine.
Engine oil? Synthetic off course. No Jiffy lube thank you, I rather craw under the car and do it myself. I would never ever trust my 1990 on a Jiffy place , Let along if I had a Killer 2002 LS 430.
BTW, Congratulations on your purchase, I'm sure you will keep it way longer than 8 years,