Transponder codes have just been changed to 7000 in Germany, too.
Compared to France (have not flown in the U.K. yet, too much water in between...) german airfiels are more controlled. Although the person on the tower is just called "info" and should just provide information, many of them feel like grown up air traffic controlers and try to tell you what to do. Ignoring this may cause some discussion. Following the published traffic pattern is essential, as many neighbours are noise-sensitive and take any opprtunity to suit for airport closure. During weekends the airspace can be full of gliders in some areas.
Oberschleissheim homes a nice aircraft museum, and is one of germans oldest airfields. Like many others, it is PPR, which means you have to phone a special number a reasonable time before arrival to ask for a permission to land. For many airfields this means some retired pilot will drive to the airport, and officially open it for you. Many of them are happy to escape their wives and their home duties for some hours, to chat with a pilot
For Oberschleissheim I do not know, if there are flying schools or maintenance companies based there, it is normally open SR-SS or 9am to 8pm, whichever is shorter. Anyway, you have to call before going there. If chatting with old german pilots, don´t mention the war
German airspace is full of class C airspace around the larger airports and restricted areas, so some route planning is necessary. Wheather is like in the U.K. except it takes a little longer before it becomes fine again. You can easily be trapped in drizzling rain for weeks north of the alps if you are unlucky. Low clouds often block several routes through mountain areas.
Rothenburg ob der Tauber is famous for the ancient city (the japanese come to take photos there), and it is within walking distance from the airport.
Coburg has a nice castle close to the airfield (you pass it by when approaching runway 12)
enjoy germany