What is a cost- and time-efficient way to set up a Berlin-based startup?

Hello everybody,

We are a Swedish-German team of four, and we'd like to set up a startup based in Berlin. We have an informal (non-written) agreement with an external investor over an initial, five-figure seed investment. The startup will be active in the B2B fintech sector, with a focus on identity management , anti-fraud solutions and credit monitoring. How do we found the company in short time and with low cost in a way that allows for the growth of the company down the road?

Thanks in advance! Best regards, Sven