I too have towed for many years , but other than towing small trailers with my 190E's , have never towed with anything as small as a C Class .
As others have stated , it is not so much about engine power as with the mass of the car being able to keep the van under control .
Re nose weight , yes you can minimise this by careful loading of the van . However , most Merc saloons have a longish overhang behind the rear axle so tend to be rated at 50 or 75 Kg .
On the other hand , if you get an estate car , they all have self levelling rear suspension and can cope with highish nose weights and keeping the outfit level which is much better for handling and stability .
On the subject of transmission , I have towed large twin axle caravans with automatic cars ( on my W123 I fitted a Kenlowe transmission oil cooler , but later cars all had a separate one anyway ) and never had any problems , with some of the cars racking up well beyond 200,000 miles .
These newer cars such as you are looking at often have the cursed foot operated parking brake , which is not a happy combination with manual transmission , and especially not when towing .