2003 C320 4-matic completely wigging out - comp/electrical!

Recently, multiple problems began occuring with my car, almost simultaneously, which makes me think whatever is happening is all connected somehow. The dealer we took the car to said that some of the problems could be connected but not all of them. However, it seems strange to me that all of these problems started happening at the same time. Please let me know if you have seen this problem before and if this can be attributed to some computer malfunction or if I would need to fix each thing separately.

1. My battery began dying. At first, it was after sitting for long periods such as a week, then it got worse so it would be completely dead after 3 hours. We replaced the battery and about 2 months later, the new battery began to die after sitting for less than 24 hours. We have tried turning off the auto lights and anything electrical before turning off the car and it did not seem to make the problem any better or worse. This happened for about 2 weeks when the weather was really cold and since it has warmed up, the problem has seemed to go away - for now.
2. Seat adjustors and sunroof periodically do not work. One day they will be fine and the next day - no power. I recently took the car to the dealer to have this looked at and they said they needed to be re-set. After taking the car home, they seemed to work fine for about 2 weeks and then the problem returned.
3. Door locks intermittently will not work with the remote key. I have to press the button a number of times before the doors will lock or unlock - but only sometimes - not every time.
4. Blinker and hazzard lights will blink randomly and sometimes not at all. The dealer said that we have a bad steering control mudule that needs to be replaced. Since this is connected to the Controller Area Network (CAN), it is causing the next malfunction as well.
5. Display lights, including radio and temperature guage, periodically all go out and the "brights" light flashes on. Then lights come back on and display gives malfunction, "Display deffective, visit workshop". Sometimes this will show a lightening bolt and other times it will show a lightbulb with the same message. At the same time this happens, I also get a malfunction message, "Restraint System, Visit Workshop! SRS". These two messages never go away and continally appear, just cycling through messages. This makes it impossible to re-set the mileage after filling up because it won't sit on the "After Re-set" view long enough to re-set. The dealer re-set these malfunctions stating nothing was wrong with these, but within 2 weeks of having the car back, these problems began occurring again.
6. Steering column will not move up or down or in or out. If the steering module is bad as the dealer says, this could probably be corrected by fixing this, however, wondering if other symptoms are connected as well.
7. Light on gas guage that blinks yellow when guage gets low continually blinks even though tank is full. Periodically, the gas gauge drops to empty, then will show the correct reading after some time. The dealer felt there was a problem with the sensors in the tank and wanted to remove the tank and replace these but the extended warranty company would not pay for this unless they could re-create the problem when the adjustor was there.
7. Seat heaters periodically turn off within seconds of being turned on. This does not happen all the time and I have not yet been able to correlate this happening when any of the other problems occur. It is just completely random.
8. 6 CD changer periodically tells me, "Magazine Empty". Sometimes when I take out the magazine and replace it, I can get it to work, but other times it will not read them.

Thanks for your help!