I'm sure German members of APUG will be able to give you lots of advice, though for film, Fotoimpex in Mitte is a must. http://www.fotoimpex.de/ I think they are sponsors here. As for where to photograph, the whole city is fascinating so very difficult to say. I book I can highly recommend which has inspired me to take many visits to Berlin is Ghosts of Berlin by Brian Ladd
This text book reflects the history of the city through it's architecture and planning, especially during the last hundred years.