Hi Ann,
Welcome. You asked for opinions, and there are many on this forum far better placed than I to offer a view on restoration. I bought a '66 230SL that was ok-ish on the surface - good paint, OK interior, OK chrome, but which had not been well maintained. I've therefore spent the last 8 months getting it on the road, and taking it off again to fix stuff. So the work does take a while to do, but then, I also have a day job and can only work at weekends. My point is that there will be delays getting parts, etc, but if you're paying top whack (are you?) I would have thought you should see real progress. As for painting the car, it does not take long at all - but getting it ready to paint can take a very long time. Preparation is vital and if rushed the finish could be poor. It depends on how much restoration of the body needs to be done first. And how much you're paying.
The horns are located under the car at the front. Stick your head underneath the front bumper and you'll see them just forward of the front wheels and spread apart - I've attached a photo, below; the horns are the 2 prominent round things. It's odd that they asked if you want to sell them as they don't fetch a premium like the lights or chrome. Your restoration will result in some old parts being taken off and replaced, so they may remove bits, but in Germany when that's done, the old bits are always given back to you at the end of the work.
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Bottom line: good restoration takes time and needs to have lots of money thrown at it; I guess the more you pay the faster the work is done assuming the shop is very good. Same with a good paint finish. I suggest you ask around here and see who lives near your shop and get a view on them. Also, communicate with the owner. At the end of the day, if you don't trust the shop and have tried to talk it through, I'd take the car away and get a recommend from someone on this forum.
Good luck.
JH
