many 123 questions - desperately need help!!

I have been driving an '81 280E (w123) for the last few months, it is my first car. The car was in fair condition, most records are left from the previous owner. A friend of my dad's, a mechanic who worked with mercedeses for over 20 years, helped me fix up the car a little, putting in new tie-rod assemblies, new oil filter/oil change, various other not too-major things. The problem is that he moved, so I can't get help from him anymore (I intended to start working seriously on the car in february/spring, with him). I don't have the money to take the car to a mercedes dealer, and all the other mechanics in my area are crooks or don't know anything about mercedes cars. I was wondering if anyone on here could help me with these questions? I know many are stupid or very basic -
first the routine 123 problems - my vacuum sytem stopped working; it used to be that when i hit the ignition, all the doors would unlock, and when i locked the driver door they would all lock, but now nothing works. Is this a serious problem, or just a faulty vacuum somewhere (I'll test them all eventually).
The A/c also stopped working. Generally, what is needed to fix faulty 123 a/c's, a compressor/some freon if i'm lucky?
And, of course, there is a LOT of play in the steering wheel. It moves a good 3 inches to the right. I have new tie rods, new, thicker tires, so do i need a new steering box? Is that very expensive?
Now the more serious problems -
after coming to a stop, when i accelerate, then let go of the gas pedal, the car rolls, and i hear a thump noise coming from the back of the car. Is this a transmission problem, or something less serious?
Finally, this may be just the car's age, but during the winter in the morning the car's movement is very jerky for a little while. It helps if i rev it up pretty hard. Is my idle speed too low?
Thanks a lot in advance, any help is appreciated. I really want to fix up this car! (by the way, in my signature it says new intake/exhaust, i never got a chance to put the parts in my car; i sold them)