1. The ac works and blows somewhat cold, however I would like it to be colder. It has already been converted to 134A, so can I just buy a can of the stuff and recharge it?

Have the system inspected, both for system pressure, leaks, consider a system refresh with a new drier.

2. The air and heat blow almost completely out of the two middle vents. The far left and far right vents are VERY weak or don't blow at all. What could be the cause of this? If I shut the middle vents the side ones do blow, just not when they are all open.

You may have an issue with the hvac system, since you should not be getting any heated air through the center vents. Mercedes during this period didn't think it was a good idea to have heated air from the center, only the sides, footwell and upper dash vents get air heated by the heater core. The center vents only get ambient temp and air conditioned.

The flow to the outer and lower vents are controlled by vacuum powered "doors" which open or shut depending on your push button selection. A faulty vacuum connection (unlikely) or a worn out vacuum valve (more likely) will cause a door to stick open or shut.

Bad news . . the whole dash and center console has to come off to access the vacuum valves.

3. I let the car sit and idle for like 5 min and noticed that the electric fan came on. Is this a normal occurrence? (It was about 90 degrees today and it was after an hour long drive)

Your engine uses a viscous coupling clutch to activate the fans, unlike early 4 cylinder engined models that used a temp sensor activated fan clutch. So long as the fans come on to keep the engine temp at a reasonable temp (lower than 110-112C) it's likely working okay.

4. I noticed that as it was idling, the outside temp. gauge kept climbing up, eventually reaching about 104 degrees. However, It was not nearly that hot outside. Once it was driving it was displaying a good reading, just not idling. What could be the cause of that?

The outside temp/ambient temp LCD uses a license plate holder mounted sensor, because the sensor is designed to warn a driver of road temps that are near freezing and the ice hazard. It could be that the temp was reading properly for the area, or the sensor is defective.

5. The car seems to look and run great, but it didn't come with any maintenance records. Is there anything I should do right away, or the near future, to the car?

The M103 six is somewhat notorious for head gasket leaking, so watch out for oil sludge in your coolant. Without records, consider starting service to create a baseline date for all fluids, including the ps fluid, brake fluid, differential lubrication, coolant, trans fluid . . . also the sunroof grease.