My dad and I have raced cars for 30+ years. We've blown up our share of motors, and I have disassembled and rebuilt countless motors. AMSOIL is the best. The quality of thier detergents are just amazing and don't break down. We put 200 hours on our last motor with no problems. the motor produced 285 HP stock and now produces over 850. Anyone in racing will tell you 200 hours is A-lot.
Mburnikas is also right about changing the brake fluid. It's not really about the fluid breaking down, it's about moisture in the lines and reservoir. Also because the car is more than 5 years old I would replace the radiator fluid,and do a fuel system cleaning. If gas sat in the tank along time there could be alot of tarnish on the valves, and injectors. One other thing I would do is a tranny fluid change. Do that every 30,000 miles. It will prevent the tranny fluid from thermal breakdown and pitting the gears and speedbands etc.etc. Once they get pitted and space, then you have to stay with the same fluid from then one.
I would skip the warranty. There are many ways for a warranty to screw you out of money. For example, you take the car to the dealer and they "hear something in the motor". The warranty won't pay for "exploratory diagnostics." So that will come out of your pocket. Then say they find that the flywheel needs to be replaced. ( I know, this is just an example.) Lexus may charge 1200 bucks for that part, but the warrantee payout may only be 800. You'll have to pay the difference AFTER the deductible. Also, most warrantee's only allow for a certain amount of "labor per hour". So if Lexus charges 150 an hour, but the warrantee only pays 65 an hour, again the difference will come out of your pocket. I'm not saying all warrantees are the exact same, but most of them sell on the basis that most people won't even think of these questions. You have to ask very specific questions when it comes to the quality of some of these "extended warrantees."
Nice purchase by the way. Definately a diamond in the rough.