This thread is of interest to me too, I plan on moving to Berlin in late April!
I have been there a few times and I have a bunch of friends there already through a different hobby.
It really is the most exciting and alive city I've ever been to, I can't wait to spend years there!
I am trying to do things all legit, I looked up the list of requirements that they want you to submit to get a residence permit, which will then allow me to work legally. The list of things they want you to get is pretty easy, it's like a scavenger hunt.
The fixed gear scene is pretty thriving, I know they have regular bike polo, alleycats and track bike boutiques so you can't go wrong. Oh, and they have a velodrome, which I intend on looking into further.
I need to keep working on my German, but in time I will get there!