2000gs

Hi guys new here,just purchased a 2000 lexus gs 300 platinum series im not too familiar to them but it has 150k its really clean and runs awesome two previous owners before me never been in an accident, i was just wondering with the milage being this high was it a smart choice because i paid 8k for it, also what should i do maintainance wise to keep it running as smooth and make it last a few more thousand miles,im also interested in knowing what performance upgrades i can do after i do the reccomended maintainance thanks....