I now have gone with this Bike: http://www.simpel-ch.de/velos/ww/nuvinci_360/herrenvelo2012.html
I have this bike for a year now and I am pretty happy with it. It does not allow very sportive riding, but it is nearly maintenance-less, since the chain is fully enclosed by the protector (which rattles sometimes). The rear rack allows mounting a Basket. I check the chain every 3 Months, and there are still no signs of rust or that the original oiling has diminished.
The transmission is very good for city riding and pulling a trailer up a hill, but not so good for going fast on roads (35 - 40 kph max possible if you have to pedal).
The brakes are also very good, the only maintainence required is filling them with some special oil, and they have no problem braking the bike going down a steep hill with a fully loaded trailer.
The bike has built in lightning that is very bright, with a hub dynamo.
This is a photo of my bike in action, with full loading capacity of about 60 kg (30 kg on the trailer, 30 kg on the rack). Total cost of the Bike, as you see it here (with trailer and baskets and airzound) was 1500 €, Maintenance cost is around 30 € per year.
