-Yes, at most smaller airfields in germany You'll need cash to pay for gas and coffee. Hotels in bigger cities normally accept CCs.
-Lots of gliding activity at smaller airfields, especially on saturdays and sundays.
-lots of wind power plants and during the week on days with fine weather some occasional VFR military jet low level flying in north-western germany (military low level flying zone), so better stay 2000" or above.
-check for latest airspace changes at Berlin because the new international Berlin Airport is nearly finished and is scheduled to open this summer.
-You can find articles on most german airports and airfields on the english wikipedia website as well.
-there's an iphone/ipad-App called "VFRiNotam" for Notams
Have a great flight!