I'm on the exact same visa. It took a month from getting to Berlin to getting the visa in my hands. I hired a lady for 800 Euro to help me do all the paperwork, forms etc as it's all in German and I had no friends/family to help me through the translation process. Having done it, I think you could get away with doing it yourself - most speak at least a little bit of English. The paperwork is not really that intensive, but you can often only book appointments 1 month out at the Ausländerbehörde (where they will do your interview & process your visa application).

I'm not 100% certain if it's the same process for US (I'm Australian), but roughly I needed: - Registered address in Berlin (It's supposed to be a rental lease, but I had my airbnb host write a letter saying this was my address in Berlin). - Bank statement of savings - 3 references from clients saying that I was being paid X amount each month - Portfolio of work (web designer)