If you can afford downtime, I'd rebuild the front & rear suspension. I'd recommend stock-quality parts like Meyle or Lemfoerder. No need to go crazy with expensive performance parts like coil-overs unless you'll be tracking the car. In that case, I'd look around for a decent used set, update the springs to a rate & height you prefer, fresh Bilsteins or Konis, and finish it off with front camber plates.
The E36 is an incredibly sweet handling car with fresh rubber all around. If you just wanted to knock out the worst offenders, replace the upper rear shock bushings and the front control arm bushings. Then test the tie rods, that sort of stuff.