Beginner’s Questions: Used Corolla Verso

Hello, I asked a lot of questions recently, but now the decision has been made. A used Corolla Verso (2007-2009) should be. Budget is so at max. 11,500 euros. My driver profile, so about 15000 kilometers a year and often expressway, daily approx. 50 kilometers(no highway). Questions: What is more economical for me? The diesel with 2.2l engine or better the 1.8 petrol? What is it like with the diesel with the “freeburning”? Does that make at approx. 24km easy distance with usually 100 km/h? Can one easily retrofit a trailer coupling? Are there any things I should look at especially with the used ones? Are some years of age known errors, to which one should absolutely pay attention? Have looked at 4 Corollas Versos on the weekend which would be interesting. Unfortunately I could not drive them a sample, but I will be able to do this on Friday. There were 2 gasoline 2006/38tkm and 2007/57tkm and two diesel 2007/60tkm and at the beginning of 2008/95tkm.