Packo, if you indicate where abouts in Germany you would likely be heading and what facilities you require (fuel type, length of stay, language capability), I could look at a few potential locations which you might want to land at.
Concerning peculiarities on crossing the border into / from Germany, I am not aware of any restrictions or special procedures when flying to / from Germany UNLESS you are flying outside of the EU or to a non Schengen Member of the EU in which case you have to fly from a customs airport.
If I were you, I would look to fly to a customs airfield in France or Belgium and clear customs there. From then on, you would be flying from one Schengen country to another hence no requirements for customs - although you will still have to file a flight plan for any cross border flight (strangely, you don't have to file flight plans when flying from Austria to Germany or back....)
With regards flying in Belgium, although the airspace seems to mean you would be tree hugging to avoid CAS, if you google "VFR flying Belgium" you'll see that there have been many threads about the Belgians and how they actually encourage GA to fly at Flight Levels, the country seems a nice place for those of us who want to transit it.....