A lot of auto manufacturers recommend premium gas but they do not requiring it.So its up to u.Most likely u not gonna notice a difference between regular vs premium.
Lexus recommends 5000 mile service intervals for LX470.Consult the owners manual.If u wanna keep the car in good shape go by the book with the maintenance.
Few thing to look out,front CV boots are known for failing,water pumps might leak.If the car needs a front brake job the rotors require to be resurfaced,that means that the bearings need to be repacked,so its gonna cost some money to do that.
Should be due for timing belt replacement at 90 000 miles(double check in the manual).
Overall its a reliable vehicle,better than most of the vehicles(SUV's) on the road.
If u wanna purchase the vehicle take it to the dealer for a buyers inspection.