Of course, that should be 50 Hz, not 60 Hz. I'm sure you've got
all the necessary power supplies, though.

The advantage of something like peterzahlt.de is that you don't
need an internet connection, but can use it from any land line.
In a hotel, of course, it would have to have direct-dial for incoming
calls. I've just ignored the ads---no quizzing.

Latest on the strikes is that none are planned at the moment, though
that could change quickly.

I don't know to what extent rental-car demand will go up in a strike.
Certainly somewhat. However, most people on the train are commuters
and most of them ride the train for convenience and price (especially
with monthly or yearly passes) but could drive their own car if necessary.
Long-distance travellers would probably resort to flying. Of course,
some people will rent a car if the trains aren't running.

Normally, I would recommend the train over a car, especially in-town.
Note that most local rail transport, or other public transport, won't
be affected by a strike, just the long-distance trains. And they might
not shut down completely, since the train company will get some folks
who don't belong to the union to drive the engines, so it might not
be a complete standstill.

Don't know about restaurants, sorry!