Berlin is not a viable city for startups.
The problem is accomodation. You can't get a place to live. This means you can't get staff.
The reason you can't get a place to live is rent controls.
Berlin has rent controls. Landlords can choose the rent when they let, but once let, they can only increase it at a very low rate - much lower than inflation.
As a result, illegal sub-letting is the norm. The tenant wants to keep their contract, so the rent price cannot be reset, so they sublet (often without telling the owner), sometimes with a markup (which is theft).
As a consequence of all this, the supply of property is strongly discouraged and there is vast unmet demand for accomodation. When-ever a place comes on the market, at least a dozen people turn up on the day after.
If you are not there in person, *you will not get that place*.
As a result, the labour market available to companies in Berlin is restricted to people in Berlin.
This is made worse by the "SHUFA", which is like a credit history. If you're outside of Germany, you won't have one, which makes you even less appealing to landlords.
Also landlords, where the law is so against them, want LOTS of security. Three months deposit is not uncommon.
Another consequence of that is that three months notice is usual in employment contracts - which makes it harder for you when you come to get out. You can't find somewhere and then resign, because most places won't take you if they have to wait three months.
Finally, note that the actual consequence of rent controls is to depress wages. Wages in Berlin are low, because rents are low. This reduces costs to companies in the rent control area, and so makes the more competitive; but at the same time, reduces the average quality of staff they can obtain, which reduces their competitiveness. In other words, it makes no sense. I think it's done because people imagine it gives them more money and politicians play along with it.
If you look at AirBnB, rent prices are two to three times higher - these are the real rents. This also means you cannot use AirBnB, if you're trying to take a job in Berlin, because you cannot afford it on your salary.
The local Government practically banned AirBnB anyway, last year. This always happens in places with rent controls, because more and more people let to AirBnB because it's worth so much more than the prices forced by the Government. Results is that it has to be banned, and then we all go back to the accomodation market being totally borked.
So, in short, don't come here. You can't get a place to live. Berlin cannot take off as a center of anything unless it fixes its accomodation market.