On the glow plugs:

You either have a bad relay or a bad plug or two. However, the symptoms you are experiencing are most probably caused by the 80amp fuse in the glow plug relay not making contact. There may be a very small hairline crack in the fuse which you cannot see. The thing to do is take a screwdriver and bridge the connection where the fuse is (just lay the shaft of the screwdriver across the two screws and jump in the car and turn the key. If the light comes on every time over a few cyles of the key on and off, replace the fuse.

The relay is in the driver's side inner fender well. A Black box with a black plastic cover on it. When you take the cover off, you'll see the flat fuse in there along with two other connections and another wire which remains hot all the time (even with key off, so be careful!). If you're iffy about working on the relay with that hot wire right there, disconnect the negative battery terminal.

On the oil pressure:

Sounds right. It will remain at 3bar when cold but will gradually drop as low as 1.5 bar when at hot idle. It should rise immediately upon acceleration.

On the fuel gauge:

Either a bad sending unit or a bad gauge is the culprit. In most cases, the sending unit is at fault.

On the front end noise:

I would need more description before being able to offer a diagnosis.

__________________
Regards,
Aaron