I arrived in Berlin in time for New Years Eve. Two things that are not illegal: public alcohol consumption and setting off fireworks. Supplies for these activities can be purchased at any corner store. The city is it a lot like a warzone on New Years Eve.
Don't stay it A&O Berlin Mitte Hostel. I did this for one night and it was terrible.
My plan was to stay at an AirB&B for a few nights, and if it seemed okay, negotiate staying longer term in person. This worked out great for me and I found a nice place in Friedrichshain for around €17.5 a night.
I got a membership at Betahaus while I was in Berlin, but I don't recommend it, mostly because it is just so overpriced. I ended up paying €219 for one month of 24/7 access to the space. The cost breakdown was €159 base monthly fee for unlimited access during regular hours + €25 initial sign up fee + €25 for adding 24/7 access. I also had to pay a €50 deposit to get a key to the building, but I got this back. But they didn't even have free coffee.
There are other much cheaper coworking spaces in Berlin, for ~€100 a month you should be able to get the same deal. I should have shopped around more.
I found this nice site for searching for coworking spaces, sharedesk.net. And another site for finding cofee shops to work from, workfrom.co. There are a lot coffee shops in Berlin with wifi where you can work for the cost of coffee. I recommend Saint Oberholtz and I've heard that the FabLab is a good place leech wifi.
It was really cheap and easy to be vegan in Berlin. Most döner places also sell falafel döners, which should be vegan if you get the spicy red sauce. You can't really beat €3.00 falafel döners. There are also tons of awesome exclusively vegan restraunts around the city. Most grocery stores carry imitation meats too. And I heard there is a vegan grocery store, and a vegan shoe store...
There are also many squat/housing co-op/intentional community like places throughout the city that offer (usually vegan) dinners for really cheap. These are indexed at Stress Faktor's Küche für Alle.
Berlin Strength is a vegan power/weight lifting gym in friedrichshain. "vegan gym" means all the supplements they sell are vegan. And all the gym equipment is vegan, so the lifting belts, shoes, medicine balls, benches, etc. are leather free. A membership for all of January was €30, it is usually slightly more expensive, but still cheap. It had a really great "no bros allowed" vibe, leftist stickers everywhere, and unisex lockerroom. I love this place and wish there was something like it in Austin.
Every Tuesday there is a cryptography stammtisch (a stammtisch is like a German meetup).
There are many tours around the city, I was lucky enough to be show around by a friend who is a tour guide. I got the "street art" and "general Berlin history" tours, there are also cold-war, WW2, and other tours which you can sign up for at most hostels. There are is also a Refugee Voices Solidarity Tour, which is a tour given by refugees of the places that have been central to the current refugee crisis.
Of course, there are clubs. I visited Berhgain, KitKat club and a few other places. If you want to get in to Berhgain, wear lots of black, dress down, and just try to look really cool, but not like you're trying too hard. Also, a warning, they will search you thoroughly upon entry. KitKat's gegen night is supposed to be interesting, but I missed it.
You should also visit the legendary hackerspace c-base. It is actually inside of an excavated alien space craft that crashed in Berlin 5,000 years ago.
On this visit, I tried to be a good German train rider and not skip the fares. There were only a few days where I had invalid tickets, but I was never asked to present my ticket a single time while I was in Germany, and I rode the U/S-bahn multiple times every day. The previous time I was in Germany in 2013 I only bought one U-bahn ticket the whole 20ish days I was there, but I got caught on my last ride to the airport. This time I was buying the 7-day tickets because they seemed like the best deal.
There is no Uber in Berlin, but you can use the Uber app to get taxis. The driver is paid through the app so you don't need to give them money. A 15 minute ride cost me about €15, it is expensive.