I need to take some pics of it & learn how to post them. Neither of the rear power windows appear to work, nor does the driver's door window. Passenger door window works, although very slowly. I did notice that the rear side windows do not want to "stay up" at the top where they'd contact the rubber seal. Instead they rest about a half inch down from there, just enough to cause wind whistle at speed & of course allow dust & rain to enter! I need to investigate this a little bit further. Sunroof motor works, but sunroof is inoperable, leading me to believe the cable is either broken, or somehow off its track. Power antenna is lifeless as well. Surprisingly, the Air Conditioning works! Although the heater doesnt (yet). I need to get an owner's manual for this car, which would be a real help.
On the windows, do the motors turn? If not, it could be as simple as a bad fuse or a bad switch. Strangely, on the sedans, one fuse operates the driver's side front window and the passenger's rear window, and a second fuse operates the passenger's front window and the driver's rear window. Not sure if the coupes are the same way, but my guess is they are. If it's not the fuse or switch, I have bad news and worse news...the bad news is, the front regulators are $500+ each OEM. Rockauto has the regulators listed, but I've heard that they won't work...the parts are listed at the same part number as the regulators for the sedans, when in reality they're considerably different from one another. The worse news is, the rear regulators aren't available ANYWHERE anymore...I don't know if the dealers carry them, but neither rockauto, peachparts, nor autohausaz carry them...and IIRC on the coupes especially, they're common failure items, so finding a scrapyard replacement won't be easy (not least because there aren't all that many 123 coupes out there).
FWIW of the three M-B's I've owned, all three of them had at least one bad regulator...the motor would turn, but you could hear it thumping because it wasn't fully engaged. Seems to be a way of life with these cars...
Re: the heater not working, I have some more bad news...there's a very real chance the failure point's at the servo assembly. My best recommendation is to junk the servo...I'm not sure if they can be bought anymore, and even if they can be, they're horribly unreliable. You have two options...you could just put in a manual valve and not have control from the cabin, or you can buy an electronic replacement:
http://unwiredtools.com/accii.asp ...sadly, even at $700, it's still considerably cheaper than getting a replacement servo, and it'll last a lot longer.
One option, if you can find a donor car, would be to swap out the entire climate control system...the electronic system used on the '81+ cars is considerably more reliable, or for simplicity's sake, you can find a 240D with manual climate controls and never have to worry about it again
What position is the antenna in? If it's down, can you grab onto the top of it and pull it up while a helper holds the switch inside? While the motors do fail, my experience has been that it's more common for the mast to be unlubricated and eventually seize up enough that the motor can't push it anymore. If that's the case, it's not too difficult nor expensive of a job to replace the mast. If it's the motor, I actually have a spare motor that may work for your car (although there was more than one motor, so I can't say for sure).
I have yet to deal with a problem with the sunroof, amazingly enough...but my guess is you're right about something being broken in the linkage between the motor and the roof, be it the cable or a connection point. The sunroof could also need lubrication...I would suggest searching on how to do that; it's important to lube in the right places and to not over-lube, and it's especially important to use the right stuff.
Hopefully this car works out for you...I presume that everything in the drivetrain's happy at this point?