personally i'd rather have one that has only done 50k than 120k, but any lexus owner will tell you that these cars like to go forever, so yes a good service history by 120k would indicate the car has still plenty of life left in it
I have an SE, but only because insurance was twice as much for me to get a sport, due to my lack of driving experience, If you can afford to get the Sport as opposed to the SE, get the Sport, since you are looking to buy a used one, you will find Sport models and SE models are pretty much the same price range
check the wheels for corrosion if the mileage is high, clean them regularly to prevent further corrosion
the cd player was changed around in 2000 as far as i'm aware, if not, late 99, mine's 2000 with the newer system, and every 99 i've seen has the older one, however mine wasn't working when I bought it, despite Lexus changing the stereos after 99, they hadn't fixed the common problems, I was lucky to find one on ebay for £100 that worked to replace mine (been fine since)