i have not been in frankfurt for long time each trip. the city was mostly destroyed in ww2, so everything rebuilt is streamlined after the main factor of this city, money.
the soccer fan-community is quite strong, local rivalery with other clubs and their fans (so be careful what you say about soccer clubs or the possibility to end in a plasic bag is high). im personally not involved in soccer fandom at all.
what kind of phd or why frankfurt? if you want recommendations which fit your specs, someone might have something if the goal is to do it in germany ;)