1. Are there any ways to mount a lighter set of front and back seats?
When yousay lighter do you mean in color or weight. Your seats are manual, instead of the later electric, so they are already rather light. I am not sure but I believe the e30 manual sport seats might be a little lighter. If you want a lighter color well there are different interiors.
2. My fan system . Ehn you say fan do you mean the one for the air or the one fore the heat? Both do tend to die. If the one for the heat you h ave to replace the one behind the firewall. There are 3 differnt kinds, so you have to pull it out before buying one. IF the one for the AC you have to take apart the center consul to get to it.
3. sunroof are both out, looks like trouble under those fuses. Does it move at all? or does it just get stuck? It could be that the nut is loose in the motor. Youcan tighten it with the allen wrench that can with the car. If it does not move at all it could be that the motor is dead, I do have one for 15 plus shipping. \
4. Is it possible to get rid of the mass airflow sensor? It is a AFM not MAS, you would have to change the a lot to get rid of it. Also do not both getting another airbox because unless you pay a lot the factory one is the best .
5. Any success with cam timing adjustment? Not sure
6. Speedo and odo are out, tach works just fine; where should I start?
Power antenna is out, is this common as well? This is common the instrument board starts to die because of age and there are small batteries on the board which leak and damage the board so things stop working. You can either buy another cluster and put it in or you can take it apart and get another mother board and put it back together.