1) Some people prefer the student life at Oxford, others in Germany/elsewhere. You can't generalize that and forget that also only focusing on the UK a lot of people e.g. prefer going to London and "don't even" apply to Oxbridge. And Freiburg isn't big enough, so that you will have to commute over long distances, probably he would just have a bike, because it is sufficient to go from the university to the university sport. It comes also down to your own preferences and to the people you will meet. (Btw not all the colleges/accomodations are so close to the department, that you don't have to "commute" in the same way, as in towns like Freiburg.)
2) On thing is pretty clear: Oxford will loose in nearly every competition with German universities(one even has its own brewery) considering the beer. (And not everyone wants to drink the cheapest beer, he can get.) More usual woul be between 1,50€ and 6€ (1,50€ half a litre of "Helles" at student parties to 6€ for 1 litre at a "Volksfest", with Weißbier, Starkbier, Pils etc. in the middle) ... Not that I would place my decision on beer prices, that is of course ridiculous, but not uncommon. The cheapest meal is 1€ to 4€ for being satisfied at the student cantines usually, supermarkets are definitely cheaper than in the UK.
3) Oxford is a European University.
4) I know, it largely depends from department to department, but e.g. I never had problems with office hours (wether regular or not) and even found me one time in a 2:1 position considering questions about exams. (I mean two from the teaching stuff and one student.) You will find all, like you find all varietians in the UK, or any other country.
5) To the TS: As German universities aren't that expensive and you have two years for your Master, which allows you to settle down, maybe you could find a possibility to get into courses in other departments, work as a student research assistant(not allways easy, but worth) to get a little bit out of the "strict economics" route.