First up, Berlin seems pretty hard to get work in general - I've been looking into it a lot myself and despite speaking pretty good German, qualifications, a strong career background & work experience, I'm not as confident as I'd like to be about being able to arrive unannounced and get doing the work I want to do. For more specific queries, check
http://www.toytowngermany.com/forum/index.php?showforum=85 , there's a lot of relevant info in the pinned topics aimed at and asked by (non EU) people in a similar situation to yourself. Teaching English on a freelance basis is often a starting point, but with the amount of Irish, British, etc. to compete against, you'd be in a saturated market.
I'm not an immigration expert by any stretch of the imagination, but I
think that if you set yourself up as self-employed in the EU, it helps a lot with getting a residence permit - if you're on a holiday visa, you get to stay 90 days in any 6 month period. Also, the general rule of thumb is that if you land a job where the employer sponsors you, your residence permit is tied to that job, so if you quit, you're fucked.
Hope that helps.