its a pretty straight forward and simple job to do with the right tools........
you should probably expect about 4 hours or so labor from a reputable mechanic.
yes i would stick with the OE equipment, as not to effect the ride the ride quality of the car........
shocks and strut replacement is a very general maintence on these cars, although they do last quiete a long time, but generally if you are into the 100K range or over, its about that time......
after market shocks and struts for example Tokico brand, although can be had for really cheap, they are a little too rigid for the LS, it all depends on your preference, Tokicos are very firm, and provide a much firmer feel than OE for more responsive handling..........but you will loosing some or most of the "floating" smooth feeling that the LS is notoriously known for......
i've personally road in both applications, same year LS, around same miles, and i prefer OE..
good luck