Hi Nick
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
http://www.amazon.co.uk/Ghosts-Berli...4621995&sr=1-1
This text book reflects the history of the city through it's architecture and planning, especially during the last hundred years.
Viel Spass!
Mike