I have a '90 300e. Not sure what differences there are but here is what I know about mine:
1) Most noticeable fix for my rough idle was replacing the engine mounts, although distributor cap, rotor, and plugs (gapped wide) also made a diff.
2) Mine too burnt about a qt of oil every 1500 - 3000 miles. No smoke. No leakage for a long time, then head gasket. No oil loss at all now and I think what I had before was from the valve guide seals (which can be replaced without pulling the head if I recall correctly).
3) My car has a mark between 80 and 120 deg. The 120 spot has a white mark adjacent to a redline mark at 120. If yours is getting anywhere near 120, I think that you have a problem -- possibly the aux fans are not running. If this is the case, you should get this checked as substantial damage to the engine may occur. Normally my aux fans kick in around the temp indicated by the mark between the 80 and 120 mark. Once the fans kick in, the temp lowers quickly several degrees and then the fans cut out until the temp rises to the mark again.