Ask HN: Tips or Advice for Freelancer in Berlin?

I'm hoping some german HNers can help me out here. I've been living and working in Germany for the past year and have a Aufenthaltsgenehmigung through my wife. Anyways, I'll be moving to Berlin over the holidays and have a good opportunity to start up freelance dev work. I've done this before in the US and Argentina, but there the taxes and other issues such as insurance seemed relatively simple to me compared to all the long Amtsdeutsch stuff I've been reading over the past couple of weeks. The main thing I can't seem to find is how expensive it will be with the insurance. Anyways, I'd be really thankful for any tips or advice any one could give me.